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The Claremont Killer

Chris_Halkides said:
Jane Taupin, the author of a number of books on DNA forensics and the coauthor of a book on the forensics of clothing, wrote, "The possibility of the crucial fingernail DNA evidence being contaminated has been raised by the defence at the start of the trial. Four other exhibits in the matter were shown to be contaminated with DNA from PathWest scientists. An intimate swab from the second deceased Jane Rimmer was analysed by PathWest in 1996 with no male DNA result, but later found in 2017 by Cellmark to have an almost complete profile of a male Pathwest scientist involved in preparing the evidence. An intimate swab from Ciara Glennon also yielded an almost complete profile of another PathWest scientist involved in testing the exhibit between 1997 and 2001. Fingernail samples from Jane Rimmer were found by Cellmark to have a DNA profile of another PathWest scientist who was not involved in testing but standing nearby. Two DNA results from branches at the crime scene of Jane Rimmer tested in 2003 years later yielded DNA of another PathWest scientist who examined them."

Ordinarily fingernail DNA evidence is highly useful, in part because so many studies have been done on it. Based on the case of Gregory Turner, I would say that when a sample is contaminated with a forensic worker's own DNA, it was by definition mishandled and should not be considered as evidence. The Australian cases of Farah Jama and Jaidyn Leskie should are cautionary tales with respect to DNA contamination. I am not offering an opinion on the overall innocence or guilt of the accused.

EDT
"Earlier, Mr Bagdonavicius was questioned about the role he played in selecting and preparing a series of "negative control blanks" to be sent to New Zealand, where additional forensic testing was being carried out on the evidence by an agency called ESR.

The "blanks" were supposed to be control samples that did not contain any traces of DNA, however, four out of the 21 samples tested at ESR were contaminated." abc

Here is an article that is skeptical of contamination in this case, although it lists one counterexample to its thesis.
Click to expand...


From what I understand, none of the samples that were found to be contaminated with DNA from PathWest employees formed part of the prosecution evidence because they didn't contain DNA from Edwards. The only DNA that linked him to the murders was from fragments of Ciara Glennon's fingernails that were initially thought unsuitable for analysis in the 90s, and had been stored for many years in a sealed container marked 'debris'. Those samples didn't contain DNA other than from the victim and Edwards. The defence seems to be relying on an argument that all samples from PathWest should be considered suspect due to the number of other errors uncovered. The critical sample was analysed with a low copy number technique, which I understand increases the risk of detecting DNA resulting from contamination.

The proposed source of the contamination was the sample taken from the rape victim. The prosecution was emphasizing the point that no DNA from the rape victim was detected in the sample. I never saw any very clear sequence of the handling of the samples reported in the news so it's a little hard to follow, but I gather that there was no evidence of the samples being handled around the same time. The defence had been expected to call it's own DNA experts but didn't, and the case closed a few minutes after the prosecution wrapped up.

It will probably come down to whether the judge decides there is reasonable doubt about the sample. There is other evidence, but I don't think it's strong enough on it's own.
 
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more thoughts on the negative controls

The prosecution's...interpretion...of the DNA contamination is that because the most important samples were not contaminated, there is nothing to worry about. I have not seen enough reporting specifically on the question of the positive results from four negative controls to be confident in the proper interpretation of this result. A negative control is typically used to show the presence or absence of gross, as opposed to sporadic, contamination. When a negative control shows a positive result, one typically has to redo the entire batch. There is only one exception to this rule that I have found, and it is a very narrow one. We discussed negative controls in the Avery thread. I would like to know which batches were associated with the negative controls that were positive. Any experienced independent DNA consultant could have pointed problems like this out. I don't understand why the defense did not make a detailed presentation.

Perhaps the lab should be audited. Other cases might be found in which the work is questionable enough that an innocent person was convicted.
 
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I didn't see a lot of detail reported on the contaminated control blanks. Most of the news reports mentioned blanks being contaminated but didn't clearly explain their association with the crucial evidence. There is some discussion of the issue on this trial podcast site. I haven't listened to the full 37 min podcast yet so I don't know whether it provides any detailed information about the batches.
 
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two kinds of negative control experiments

On pages 76-77 in Advanced topics in forensic DNA typing: methodology John Butler wrote, "These controls typically include a "negative control," which is the entire PCR reaction mixture without any DNA template. The negative control usually contains water or buffer of the same volume as the DNA template and is useful to assess whether or not any of the PCR components have been contaminated by DNA (e.g., you or someone else in your lab). An extraction "blank" is also useful to verify that the reagents used for DNA extraction are free from any extraneous DNA templates."

It occurs to me that the controls in question might have been extraction blanks, but I am not sure.
 
I found something referring to the control blanks on the WAtoday reporting of the trial, under 'State seeks to clarify impact of contamination on results'.

'Mr Hollingsworth is re-examining Dr Harbison and asking about which fingernail samples were impacted by the contaminated 'blank' or control samples.'

'She said AJM41 and AJM46 - which returned the presence of a female DNA profile - were in a batch with a contaminated blank. She said this means the SGM+ results become invalid, however the Y chromosome testing, which detected no male DNA, is still valid.

The critical exhibit AJM42's blank was blank. '

It's not the clearest wording, but I was wondering if this means the crucial sample was in a separate batch that did not have a contaminated blank.
 
Chris_Halkides said:
Jane Taupin, the author of a number of books on DNA forensics and the coauthor of a book on the forensics of clothing, wrote, "The possibility of the crucial fingernail DNA evidence being contaminated has been raised by the defence at the start of the trial. Four other exhibits in the matter were shown to be contaminated with DNA from PathWest scientists. An intimate swab from the second deceased Jane Rimmer was analysed by PathWest in 1996 with no male DNA result, but later found in 2017 by Cellmark to have an almost complete profile of a male Pathwest scientist involved in preparing the evidence. An intimate swab from Ciara Glennon also yielded an almost complete profile of another PathWest scientist involved in testing the exhibit between 1997 and 2001. Fingernail samples from Jane Rimmer were found by Cellmark to have a DNA profile of another PathWest scientist who was not involved in testing but standing nearby. Two DNA results from branches at the crime scene of Jane Rimmer tested in 2003 years later yielded DNA of another PathWest scientist who examined them."

Ordinarily fingernail DNA evidence is highly useful, in part because so many studies have been done on it. Based on the case of Gregory Turner, I would say that when a sample is contaminated with a forensic worker's own DNA, it was by definition mishandled and should not be considered as evidence. The Australian cases of Farah Jama and Jaidyn Leskie should are cautionary tales with respect to DNA contamination. I am not offering an opinion on the overall innocence or guilt of the accused.

EDT
"Earlier, Mr Bagdonavicius was questioned about the role he played in selecting and preparing a series of "negative control blanks" to be sent to New Zealand, where additional forensic testing was being carried out on the evidence by an agency called ESR.

The "blanks" were supposed to be control samples that did not contain any traces of DNA, however, four out of the 21 samples tested at ESR were contaminated." abc

Here is an article that is skeptical of contamination in this case, although it lists one counterexample to its thesis.
Click to expand...

That's a common defence strategy: any contamination whatsoever means the sample is unreliable and needs to be discarded.

Of course I fully understand why the defence wants to use that, if you eliminate the DNA evidence you don't need to explain how your clients' DNA came to be on the victims' fingernails, which is usually a problem that usually can't be solved outside of taking a plea deal.

The usual standard for laboratory contamination is to extract the samples from known donors (i.e. the swabs of suspects) in a separate room and when possible by different people (usually less qualified, students and techinicians) than the samples from the crime scene. Other steps may also be taken, using a different facility would be best but that's usually not possible, so the steps are to use different rooms, different people and different machines, in that order. That should make the transfer of DNA from the known sample outright impossible.

Controls help, but they only tell you there is no systemic contamination with DNA from a megadonor. If there is it should be widespread. German police for years searched in vain of a mystery murderer that was showing up in DNA samples from countless murder scenes. They knew nothing about the killer, just that it was a woman who was implicated in dozens of unconnected murders all over the country.

Then they figured out a fancy brand of swabs they were using in some investigations wasn't sterelized because they weren't intended for forensic use, "the mystery murderer" was a package line worker that left her DNA on the product. It wasn't a problem for the manufacturer because it never advertised their product as sterile or DNA free, but it was a huge issue for the (incompetent) police. Many cases had to be looked over and evidence discarded, thousands, perhaps millions of man-hours went to waste over improper and inadequate use of negative controls.

But anyway, contamination with DNA from laboratory personnel happens from time to time, even though every step is taken to minimize the incidence. That doesn't mean there was transfer of DNA from two samples that were handled in different rooms (that's mandatory, if you want to be accredited), probably by different people and on different days. Any such contamination would have to be found by the negative control.

Defence going the contamination route because a lab worker showed up in some of the samples is akin to "Collusion is not a crime!". It works sometimes too.

McHrozni
 
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The persistence of DNA in an office

Fonnelop et al., Forensic Science International: Genetics 29 (2017) 48–60. http://dx.doi.org/10.1016/j.fsigen.2017.03.019

“The [20] participants were all handed T-shirts, one for each of the experiments they would participate in. They were instructed to wear each T-shirt for 3 h. This gave an opportunity to both deposit their own normal background DNA but also to collect “foreign” background DNA from their immediate environment. Participants were instructed not to have any direct physical contact with others during the period."

“In addition we observed one occasion of secondary transfer from a co-worker who had been on leave for two months. This means that sufficient amount of DNA for transfer could persist in the office environment for two months or more.”

The period of 14 months is relevant to this case. One could argue that DNA might persist longer in an office than a lab, but it would be better to be able to demonstrate that point.

There is another aspect of the contamination issue that is worrying. "But Mr Egan said the laboratory would have been cleaned hundreds if not thousands of times in the 14-month period from February 1996 to April 1997 and PathWest had not identified any possible way for the fingernail samples to have been accidentally contaminated by the rape samples." link

Yet it is often not possible to specify the mechanism of transfer: "He [Mr. Egan] said PathWest had been unable to pinpoint the exact way her DNA had been transferred to the twig, but had concluded it must have been through equipment used during the processing of the samples."
 
Chris_Halkides said:
Fonnelop et al., Forensic Science International: Genetics 29 (2017) 48–60. http://dx.doi.org/10.1016/j.fsigen.2017.03.019

“The [20] participants were all handed T-shirts, one for each of the experiments they would participate in. They were instructed to wear each T-shirt for 3 h. This gave an opportunity to both deposit their own normal background DNA but also to collect “foreign” background DNA from their immediate environment. Participants were instructed not to have any direct physical contact with others during the period."

“In addition we observed one occasion of secondary transfer from a co-worker who had been on leave for two months. This means that sufficient amount of DNA for transfer could persist in the office environment for two months or more.”

The period of 14 months is relevant to this case. One could argue that DNA might persist longer in an office than a lab, but it would be better to be able to demonstrate that point.

There is another aspect of the contamination issue that is worrying. "But Mr Egan said the laboratory would have been cleaned hundreds if not thousands of times in the 14-month period from February 1996 to April 1997 and PathWest had not identified any possible way for the fingernail samples to have been accidentally contaminated by the rape samples." link

Yet it is often not possible to specify the mechanism of transfer: "He [Mr. Egan] said PathWest had been unable to pinpoint the exact way her DNA had been transferred to the twig, but had concluded it must have been through equipment used during the processing of the samples."
Click to expand...

This is why the contamination defence works sometimes, you confound the jury with a theoretical possibility and leave the obvious questions unasked.

Here's one: How come the fingernail samples, the ones that would contain assailant's DNA, were contaminated, but not other samples?

If his DNA persisted in the lab then you'd expect it to be picked up by many samplings. Yet somehow it only contaminated the samples that would implicate him in the crime, but not any others. Conveniently there was no other DNA in the sample either, because any such contamination would be truly minimal (though possible). If there was a different perpetrator and there was his DNA, there is no way such a minimal contaminant could overwhelm the assailant's DNA. At worst you'd get a mixture of two DNA profiles, that you'd be able to deduce come from your suspect and someone else.

Personally I'd rather go with "police set me up". It's less likely to work, but also less embarassing to listen through. Setting someone up is trivially easy if amplified DNA samples are stored (as is common). You just need to find the tube, thaw it and take out half a microliter or so. You're in and out in ten minutes, no one will ever know. I mean sure, "there was a persistent contamination in the laboratory" is more likely to work on the jury that never knows to ask the follow-up question, or at least isn't able to deduce the defence's argument "it's up to the prosecution to prove the negative" doesn't hold water. But it's embarassing to listen through nonetheless.

By way of comparison, that defence is equivalent to "no sir, it wasn't me in the photo and the video, but someone who looks just like me and wears the same clothes and speaks in my voice and has the same accent, but the prosecution must prove it's actually me, not just someone who looks, dresses and talks just like me". That defence isn't going to work, but it's a pretty good equivalent to the persistent DNA contamination in the laboratory.

McHrozni
 
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Jane Mixer and Gary Letterman

McHrozni,

You wrote, "How come the fingernail samples, the ones that would contain assailant's DNA, were contaminated, but not other samples?" I am not sure that we know about all samples from this lab, as opposed to the samples pertaining to this case. A good deal stands or falls on what is released during a discovery process.

The laboratory of van Oorschot has been studying DNA transfer for many years. They wrote, Our forensic biology laboratory has had an EDM programme in place for a number of years in which various surfaces and tools from within the laboratory are sampled on a peri- odic basis. The items sampled vary each cycle and include those that are deemed high risk (i.e. items that may come in direct contact with exhibits), medium risk (i.e. items that may be touched just prior or during examination of an exhibit) and low risk." If Dr. van Oorschot had testified for the prosecution, I would take it very seriously. I am less inclined to take the lab's own testimony seriously. For one thing, at least one person was fired for not following laboratory procedures.

Do you think that laboratory contamination happened in the Letterman/Mixer case? If so, what do you see as the difference here?
 
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The prosecution's expert witness

I have now briefly reviewed Jonathan Whitaker's credentials and they look sound, although I still think that Dr. van Oorschot would have been as good or better. Andrea Mays reported on some of his testimony. "Dr Whitaker said the DNA found on the fingernails was mixed-profile DNA, matching both Ms Glennon's profile and that of Edwards, and both components of the DNA had degraded in the same way, suggesting they had been exposed to the same environmental conditions." This is true, but my understanding of the defense's hypothesis is that the putative contamination happened a long time ago.
 
Leiterman, not Letterman

Chris_Halkides said:
Do you think that laboratory contamination happened in the Letterman/Mixer case? If so, what do you see as the difference here?
Click to expand...
This should be the Gary Leiterman/Jane Mixer case. The best summary of this case can be found in Erin Murphy's book.
 
Chris_Halkides said:
I have now briefly reviewed Jonathan Whitaker's credentials and they look sound, although I still think that Dr. van Oorschot would have been as good or better. Andrea Mays reported on some of his testimony. "Dr Whitaker said the DNA found on the fingernails was mixed-profile DNA, matching both Ms Glennon's profile and that of Edwards, and both components of the DNA had degraded in the same way, suggesting they had been exposed to the same environmental conditions." This is true, but my understanding of the defense's hypothesis is that the putative contamination happened a long time ago.
Click to expand...

Ciara Glennon's body was discovered three weeks after her murder and had been semi-buried in bushland during what would have been fairly hot weather. The sample from the rape was taken immediately after the offence. Would DNA degrade more from a few weeks out of doors under those conditions than a couple of years stored in a lab? I remember reading this evidence before, but I thought it was referring to degradation that would have occurred prior to the samples coming to the lab, which would not have happened to Edwards' DNA if it had been transferred later. Is that plausible?
 
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A study on fingernail DNA and environmental conditions

Elaedith said:
Ciara Glennon's body was discovered three weeks after her murder and had been semi-buried in bushland during what would have been fairly hot weather. The sample from the rape was taken immediately after the offence. Would DNA degrade more from a few weeks out of doors under those conditions than a couple of years stored in a lab? I remember reading this evidence before, but I thought it was referring to degradation that would have occurred prior to the samples coming to the lab, which would not have happened to Edwards' DNA if it had been transferred later. Is that plausible?
Click to expand...
There is a paper by Nakanishi and colleagues that studied degradation of DNA underneath fingernails: DOI: 10.1016/s1344-6223(02)00109-8. "Then thumbnails of five volunteers were left in dried soil, wet soil, river water, sea water, distilled water or air for 3 months. Each nail sample was tested monthly for sex chromosome-specific repeats, ABO genotype, STRs (TH01, TPOX, CSF1PO, FES and vWA loci), and D1S80 locus. These markers were correctly detected from nails after 1 month, irrespective of environmental conditions. Thereafter, the detection rates were decreased to various degrees, except for nails left in air. The detection of longer DNA markers tended to be more difficult than the detection of shorter markers. Nails were more fragile in wet soil than in any other condition."

Some years ago I conversed with someone who had studied DNA degradation as part of his thesis. He cautioned me against over interpreting the degree of DNA decay. The problem is that there are so many factors that can lead to degradation.
 
Chris_Halkides said:
McHrozni,

You wrote, "How come the fingernail samples, the ones that would contain assailant's DNA, were contaminated, but not other samples?" I am not sure that we know about all samples from this lab, as opposed to the samples pertaining to this case.
Click to expand...

Actually there's a pretty good chance we do know that.

Every sample that returns a positive will be matched against the database of known profiles. It's called a cold hit, the police have been doing it for decades now. Every time you profile someone it goes on file, sometimes for a few years, sometimes for a few decades, sometimes permanently, it depends on the jurdistiction. Positive results with no known matches are stored permanently, every new profile is matched against the database.

If there was a persistent contamination in the laboratory he would be implicated in a whole range of otherwise unconnected cases, with zero evidence of the suspect ever being there and at least a few where he definitely wasn't there (i.e. a bank robbery while serving 30 days for drunk and disorderly conduct).

The laboratory of van Oorschot has been studying DNA transfer for many years. They wrote, Our forensic biology laboratory has had an EDM programme in place for a number of years in which various surfaces and tools from within the laboratory are sampled on a peri- odic basis. The items sampled vary each cycle and include those that are deemed high risk (i.e. items that may come in direct contact with exhibits), medium risk (i.e. items that may be touched just prior or during examination of an exhibit) and low risk." If Dr. van Oorschot had testified for the prosecution, I would take it very seriously. I am less inclined to take the lab's own testimony seriously. For one thing, at least one person was fired for not following laboratory procedures.

Do you think that laboratory contamination happened in the Letterman/Mixer case? If so, what do you see as the difference here?
Click to expand...

A bit of lingo first: known sample is the cheek swab you'll use for DNA matching, an unknown sample is stuff that should contain DNA from a person of interest.

There's a significant disconnect between following procedures in order not to contaminate a critical sample and following procedures in order to deny the defence the ability to scream "contamination" on top of their lungs to secure acquittal. All of these studies, procedures, protocols and whatnot are about the second point, to prove beyond any reasonable doubt there was no contamination. This is nearly impossible to do because you're proving the negative, hence the hassle.

The first point, actually preventing contamination from implicating an innocent person, is non-issue. Extremely basic protocols, followed by every lab that deals with human samples (not just forensics), do that for you. Forensic laboratories do at least one better and process known and unknown samples in separate rooms. However that's to prevent widespread false alarms, not to prevent an innocent person being framed as a result of contamination. You see, it would be an incredible coincidence for a laboratory that might process 1000 known samples (swabs for matching) and 500 unknown samples every week to have a contamination from a known sample from several months ago to specific sample that was relevant to the case from exactly that individual, but not have it contaminate any other sample. That's what negative controls tell you, there is no omnipresent, systemic contamination in the laboratory or equipment or reagents or anywhere else.

Odds of a specific known sample contaminating one and only one unknown sample that is also relevant to that suspect are on the order of one in several billion or less. If it just contaminated a sample it wouldn't be a problem for the suspect, no prosecution is followed on DNA sample alone. At a minimum you also examine the alibi and in most cases people who didn't do the deed have a rock-solid alibi, plus motive, means and everything else. If you find a DNA sample that just doesn't fit anywhere, when the implicated person was obviously nowhere near the victim, ever (i.e. locked up), then you suspect contamination. The samples aren't separated because it would cause a spike in false convictions or unnecessary prosecutions, they're separated to eliminated pointless police work in chasing down leads caused by laboratory contamination.

The overwhelming majority of contaminations would look like that, they would imply random people who literarily couldn't have had anything to do with the crime. This happens just about never, which means the laboratory contamination with a known sample also doesn't happen all that often either.

But explaining that to a jury is often impossible, plus you can't prove this wasn't a unique one type event that. That's still possible, the odds are femtoscopic but nonzero and the court is supposed to interpret everything in favor of the defendant, so you do everything that is humanely possible to prove it didn't happen, then do another three steps further for good measure (thanks, CSI).

As to why you have these studies that show this is indeed possible, the answer is mundane. You see, expert witnesses aren't exactly community service, you expect to be well fed and well paid for your testimony. Having a study of some sort to back up whatever claims you make means you're more valuable as an expert witness. Rule of thumb, if defence claims laboratory contaminiation without very credible and specific evidence it really did happen - someone in the laboratory not following the proper procedure once in the past five years is not it - then the result is fine and defence is just unable to explain it. A credible claim of contamination would be the same DNA profile being found in a completely unrelated case, with zero explanation, or at least a number of false cold hits coming from the laboratory. This will be on the DNA profile and there will be a police report regarding the hit, if you can find that you can claim contamination and remain credible. If you don't have that or something as good as that you're grasping at straws.

That is not to say laboratories shouldn't do everything in their power to prevent contamination from arising in the first place, they should. I'm just saying this is a solved issue, it's not much harder that keeping the workplace cool in summer and warm in winter.

Also, don't think police framing doesn't happen. It's very easy for the police to take one of the swabs and contaminate evidence before it ever reaches the laboratory. I know of some cases when this was basically the only explanation for the quantity and quality of DNA evidence provided. It was either that or the suspect repeatedly licked the bags he used to store drugs.

But that's not a laboratory contamination or something the forensic lab can solve. The official explanation was a superdonor, which is also possible - some people just normally shed way more DNA than others.

McHrozni
 
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Chris_Halkides said:
This should be the Gary Leiterman/Jane Mixer case. The best summary of this case can be found in Erin Murphy's book.
Click to expand...

If I understand this case correctly, I would think the main difference between the Leiterman case and the current one concerns the time interval between processing the critical sample and the potential source of contamination. I understand that in the Leiterman case the samples can into the lab around the same time and were processed within a few weeks of each other. The time interval is much longer in the Claremont case. I suppose in theory the DNA sample from the Claremont rape could have survived that long somewhere where it escaped cleaning, and if a sample escapes cleaning for a few weeks it could continue to do so for longer. It's also possible that the trace could have contaminated more than one sample in the lab, but that this was only detected in the fingernail sample due to the use of low copy number methods for that sample. I would say overall the probability of contamination could be lower in the current case based on the length of time and that there was another unexplained incidence of contamination from Ruleas on the actual critical sample in the Leiterman case.

As for the probability of inferring guilt based on DNA evidence, what struck me about the Leiterman case is that there was apparently no reason to suspect him until the DNA match was made. That means that even if the prior probability of the DNA getting into the sample by contamination was low, the prior probability that he left the DNA at the crime scene would be even lower (given no more reason to suspect him over any other male who might potentially have done so). In the Claremont case, the Karrakatta Cemetery rape had already been linked to the murders on the basis of similarity in the location and characteristics of the offences and fibres found on the rape and murder victims. That means that even had no DNA been recovered from the murder victims, being identified as responsible for the rape would still have meant Edwards would be under suspicion for the murders (although harder to prove without the DNA).
 
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Rex and Pad and Profile N; Leiterman

I found an old blog post of mine which mentioned both the Leiterman case and Profile N in New Zealand. I will quote only a small portion here:

Michael Strutt reported, “One caught up in the testing was a mild mannered Christchurch man who had been assaulted outside his local, the Hagley Arms Hotel, on 23 April 1998. Police had taken blood in order to eliminate his DNA from samples taken from the scene of the assault and sent it to ESR for testing. The result of this test came to be dubbed 'Profile N' by the inquiries which were to follow… The Christchurch assault victim was subjected to 'extensive police inquiries' for more than three months and his financial records were seized. This established what he had claimed all along, that he had not left Christchurch around the time of the murders. In fact he hardly left Christchurch at all… Although they never discovered exactly how the mistakes had happened they did determine that the 'Rex' and 'Pad' samples had been accidentally contaminated with DNA from Profile N at an early stage of processing at ESR's Mt Albert laboratories. Extracts from them sent to other laboratories for testing also returned Profile N. Numerous recommendations for improving oversight, record keeping and even laboratory ventilation were made....The fact that the lab in question met the audit requirements is evidence that simply following accepted protocols does not guarantee that contamination will never happen. The lack of the determination of an exact mechanism of contamination is consistent with Dr. Kessis’s caution in the Mixer case above. People who argue that Amanda Knox and Raffaele Sollecito are guilty sometimes demand a mechanism of contamination; unfortunately, this cannot always be determined.”

I was surprised by certain aspects of the Letterman case; for example, that Ruelas's sample was sent to another lab. Erin Murphy wrote, "Leiterman's sample came into the laboratory on February 22, 2002; the evidence in Ruelas's case was processed the day before. Leiterman's sample was first analyzed between July 17 and July 23; Ruelas's reference sample was submitted on July 19 then sent to an outside lab for testing. The Mixer evidence was processed at the lab between March 26, 2002, and April 9, 2002." p. 57, Inside the Cell: The Dark Side of DNA.

So it seems as though there were some time gaps between various samples entering the lab or being processed. The link that I used for Michael Strutt's reporting on Profile N may be dead.
 
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Elaedith said:
If I understand this case correctly, I would think the main difference between the Leiterman case and the current one concerns the time interval between processing the critical sample and the potential source of contamination. I understand that in the Leiterman case the samples can into the lab around the same time and were processed within a few weeks of each other. The time interval is much longer in the Claremont case. I suppose in theory the DNA sample from the Claremont rape could have survived that long somewhere where it escaped cleaning, and if a sample escapes cleaning for a few weeks it could continue to do so for longer. It's also possible that the trace could have contaminated more than one sample in the lab, but that this was only detected in the fingernail sample due to the use of low copy number methods for that sample. I would say overall the probability of contamination could be lower in the current case based on the length of time and that there was another unexplained incidence of contamination from Ruleas on the actual critical sample in the Leiterman case.
Click to expand...

You run at least one sample in each batch to clear up such questions. It only contains the reagents and no human DNA, so if there is any persistent contamination this will pick it up. It did not do so, I wager. Furthermore, I reckon at least some of the proper samples the lab ran came up as wholly negative too. This is incompatible with a contamination within the laboratory.

I'd say a contamination by a sample that was present in the laboratory within weeks of the crime sample being ran is less likely than deliberate framing.

McHrozni
 
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Chris_Halkides said:
I found an old blog post of mine which mentioned both the Leiterman case and Profile N in New Zealand. I will quote only a small portion here:

Michael Strutt reported, “One caught up in the testing was a mild mannered Christchurch man who had been assaulted outside his local, the Hagley Arms Hotel, on 23 April 1998. Police had taken blood in order to eliminate his DNA from samples taken from the scene of the assault and sent it to ESR for testing. The result of this test came to be dubbed 'Profile N' by the inquiries which were to follow… The Christchurch assault victim was subjected to 'extensive police inquiries' for more than three months and his financial records were seized. This established what he had claimed all along, that he had not left Christchurch around the time of the murders. In fact he hardly left Christchurch at all… Although they never discovered exactly how the mistakes had happened they did determine that the 'Rex' and 'Pad' samples had been accidentally contaminated with DNA from Profile N at an early stage of processing at ESR's Mt Albert laboratories. Extracts from them sent to other laboratories for testing also returned Profile N. Numerous recommendations for improving oversight, record keeping and even laboratory ventilation were made....The fact that the lab in question met the audit requirements is evidence that simply following accepted protocols does not guarantee that contamination will never happen. The lack of the determination of an exact mechanism of contamination is consistent with Dr. Kessis’s caution in the Mixer case above. People who argue that Amanda Knox and Raffaele Sollecito are guilty sometimes demand a mechanism of contamination; unfortunately, this cannot always be determined.”

I was surprised by certain aspects of the Letterman case; for example, that Ruelas's sample was sent to another lab. Erin Murphy wrote, "Leiterman's sample came into the laboratory on February 22, 2002; the evidence in Ruelas's case was processed the day before. Leiterman's sample was first analyzed between July 17 and July 23; Ruelas's reference sample was submitted on July 19 then sent to an outside lab for testing. The Mixer evidence was processed at the lab between March 26, 2002, and April 9, 2002." p. 57, Inside the Cell: The Dark Side of DNA.

So it seems as though there were some time gaps between various samples entering the lab or being processed. The link that I used for Michael Strutt's reporting on Profile N may be dead.
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The DNA evidence in Knox/Sollecito case should be thrown out entirely. Not because of any laboratory or collection contamination, but because if you collect samples of a place someone lives in, there is a built-in explanation for their DNA being whereever: they lived there.

DNA may be used to establish the presence of person X on the scene. If that scene is his or her home then DNA is nearly useless to proving that yes, they indeed lived there. If all you find is their DNA, even if it's in a room they claim they never went to, there is an explanation for that - they left their DNA somewhere (perhaps from a sneeze) and someone else transported it to the room. If all you have is DNA that is useless as evidence.

Police investigation is always personal, first and foremost. You question the suspect and try to have them establish a story. Then you look at all the evidence, including forensic evidence, to see if it matches the story or if there is some bit or piece that cannot be explained by the story. I can explain the presence my own DNA in my home, thank you very much. My DNA on the handle of a knife that was used to kill the victim? It's entirely possible that someone held it with a glove, or else had very dry hands, and my own DNA remained there as the main donor.

This is far more likely than some mysterious "laboratory contamination" that only affected one sample - crucially the one that made the difference in the case.

McHrozni
 
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