Continuation - Discussion of the Amanda Knox case

[Fiona]

http://www.fbi.gov/hq/lab/fsc/backissu/july1999/ponce.htm

It appears that this problem has been recognised since 1999.

Our study questions the dependability usually attributed to presumptive tests. Throughout the process, we found that a stain that was clearly a bloodstain gave a negative result in the presumptive test. This result was obviously a false negative, a nonlegitimate negative that might have detained a perfectly viable and necessary investigation.


<snip>

The second experiment we performed demonstrates the possibility of obtaining false negatives with reagents frequently used in presumptive tests. Just as false positives are sometimes encountered, our tests affirm that false-negative results may be obtained as a result of sample contamination.

The presence of ascorbic acid may not be the only cause of false results. It is possible for a bloodstain to go unnoticed if it has had sufficient contact with a product with a high reduction strength (detergents and foods). Evidence examiners should also consider that a variety of circumstances, such as washing, rain, heat, and time, may reduce the concentration of blood in the sample, with small amounts of contaminant being sufficient to give rise to a false negative in the presumptive test. Examiners may, therefore, encounter stains that look like blood, but these stains would not be recognized as such in a presumptive test. This would give rise to a false negative in an otherwise reliable presumptive test, with the result that important evidence may be lost.

There is probably a lot of subsequent work either confirming or denying this finding.

 

[Fuji]

3) Fuji: my analogy is a good one.

No, it's a poor one because the dynamics of the two situations are greatly dissimilar. About the only commonality between the two is a heightened state of anxiety/awareness. Burglars are not in fear of immediate annihilation. Escaping prey is not hunting for items of personal value.

If you think that a domestic burglar experiences feelings more akin to a predator than prey, then ask a criminal psychologist for clarification.

I don't have one handy right now. Would you care to suggest one?

And just how many prior break-ins are you ascribing to Guede...?

I'm not assigning any prior break-ins to Guede. I've seen nothing that officially, conclusively demonstrates that Guede has a history of burglaries. I am willing to concede that he probably has some experience with petty theft and/or B&E. However, from my vantage point, this is all moot because I don't think there was a genuine burglary that night in the cottage.

 

[Kestrel]

Maybe, but I think that is quite unlikely.

I am somewhat mystified why so many people either implicitly or explicitly maintain that taking a bathroom break while in the midst of committing a burglary is a routine occurrence.

If you really think your average burglar is going to take a bathroom break while:

- alone, without a lookout
- in an interior room with no ready access to the street
- in a house where he is known to most of the occupants

then I think you are sorely mistaken.

It greatly helps to understand the dynamics of the situation if you actually try and think like a real burglar would.

If it was a choice between taking a bathroom break and soiling his pants, I doubt Rudy would think twice about finding a bathroom.

 

[Danceme]

Adding to the bra story, I think it's irrelevant how a bra is normally removed when assessing Meredith's bra with its misshapen hooks. This could only happen if considerable force were used to wrench the two sides of the backstrap apart, as in being grasped either side of the clasp and forcibly trying to pull it apart. This could have resulted in the hooks locking tighter into the loops with the assailant then manually trying to manipulate them free before resorting to cutting through the backstrap and freeing the clasp.

 

[Malkmus]

Someone stepped in blood or water/blood mixture and then stepped on the barthmat,no doubt about it. But if it was Rudy as you claim and he did it to rinse his shoe before putting it back on and going back into Meredith's room to rifle through her purse then where are his shoeprints leading from this bathroom to her room Charlie?


LJ, I suggest you actually try removing a bra before being so emphatic about how it's actually done because you are decidedly wrong.

First removing my own bra:
My hands reach behind my back facing upward. My left hand grasps the left side near the clasp, thumb under strap and fingers in front over loops, (mine is on the first set of loops leaving two sets exposed) while the thumb of my right hand pushes the clasp hook section toward and over the loop section. In so doing the tip of my middle finger pushes the underside edge of the clasp toward the thumb thus pushing the hooks out and through the loops (at this point the middle finger is firmly pressed on the hooks). This is necessary because of the tension the back strap is under.

Unclasping someone else's bra from behind: (my bra wrapped around a pillow)
Left side of backstrap to left of the clasp is grasped by left fingers sliding under strap with thumb in front, all pointing downward. Right fingers and thumb once again perform the grasping at the edge of the hook side of the clasp to push clasp toward and through the loops. This causes the thumb to have firm contact with the hooks during a movement designed to 'pick up' the clasp and push/pull the hooks through the loops on the opposite side.

To try and push two pieces of material together as you suggest, thinking the hooks will simply slide through the loops indicates a lack of experience with bra removal. This approach usually results in much fumbling and wasted effort with the wearer usually having to come to the rescue of such a hapless male, deftly removing it herself with the movements described above.

But neither of these two scenarios happened to Meredith's bra. It was ripped apart with a knife. So it seems odd that the perpetrator of this act would have needed to put any friction on the metal hooks at all.

 

[Charlie Wilkes]

Someone stepped in blood or water/blood mixture and then stepped on the barthmat,no doubt about it. But if it was Rudy as you claim and he did it to rinse his shoe before putting it back on and going back into Meredith's room to rifle through her purse then where are his shoeprints leading from this bathroom to her room Charlie?

That question applies no matter who left the print. I would suppose that the blood was on the upper part of the shoe rather than the sole.

Guede did not memorialize his every move with physical evidence, but he left a pattern of physical evidence that tells a story. The physical evidence attributed to Amanda and Raffaele, however, tells no story. It merely deepens the mystery, which suggests that the most plausible explanation is that none of it has anything to do with the murder.

 

[Fuji]

If it was a choice between taking a bathroom break and soiling his pants, I doubt Rudy would think twice about finding a bathroom.

If it was a choice between taking a bathroom break and soiling his pants, I doubt Rudy would have thought twice about finding a bathroom before he attempted entry into the house.

 

[Danceme]

But neither of these two scenarios happened to Meredith's bra. It was ripped apart with a knife. So it seems odd that the perpetrator of this act would have needed to put any friction on the metal hooks at all.

I completely agree, as I said in a later post, which is just above yours in fact, the casualty of being moderated.

 

[Mary_H]

Yes, I am this far behind, slowly catching up on reading the thread.

I think it would be more honest then to not make a positive claim on this then, call it "your theory" or something.

WHO policies are not legally binding of course.

In the US, many institutions in which people will be confined in close quarters test for Tuberculosis, despite its relative rarity, not primarily because "in case [they] are sick and they want to treat [them]," but because unlike cancer, it is infectious. The CDC apparently made recommendations (I can't find the original document) that HIV testing be made a regular part of health testing in US prisons for that reason.

Regardless, it's hardly a compelling argument when you neither cite relevant Italian law or standard practice at the Perguia prison systems.

Wikipedia cites that screening tests run false positive rates of 15 in 1000, which is rare, but hardly "extremely" so.

I am unaware of claims that Knox was told she was positive after the second test (a false positive after the second test would I agree constitute 'extremely rare', btw).

Nadeau?

I thought she was considered an unreliable source by Knox supporters (Bruce, want to chime in here?)

I wholeheartedly agree with your principles here, but your arguments here fall far short of proof of your original statements.

I stand corrected, Mr. D. I should have said "I believe," not "we know."

You are also correct that WHO's recommendations are not legally binding. They are based on concepts of medical ethics, not necessarily on national laws. Many of the indignities that were inflicted on Amanda and Raffaele were, to my mind, unethical, but not necessarily illegal.

Your objections to my post are legitimate. I need more information about this topic; some of my understanding of it may be from undocumented sources. If you have concrete information about it, I would welcome seeing it.

Also, if you agree with me in principle, what would your observations about the topic be?

Thank you!

 

[LondonJohn]

http://www.fbi.gov/hq/lab/fsc/backissu/july1999/ponce.htm

It appears that this problem has been recognised since 1999.



There is probably a lot of subsequent work either confirming or denying this finding.

The report you are linking to here also has no direct relevance to the Kercher case. Its subject is the effect of reducing agents on false negative presumptive blood tests - and nothing more than that. Reducing agents, such as lemon juice or acetic acid (vinegar) are the exact opposite (chemically) of oxidising agents such as bleach (hypochlorite) or peroxide (H2O2).

The report's authors explicitly make this point in the abstract:

"Given that the aim of our study was to demonstrate that reduction substances contaminating a bloodstain may prevent a positive test result from being observed, ascorbic acid was chosen as the substance to be used after the components of lemon juice were analyzed (Windholz et al. 1996)."

The fact that the end of the abstract makes a vague reference to other scenarios, including prolonged exposure to detergents or certain foods, is entirely peripheral to the actual subject of their paper (see the quote above). It is also somewhat irrelevant in the instance under examination in this case. The prosecution themselves allege that the knife was cleaned extensively with bleach (NaOCl), which would have denatured all the proteins (including haemaglobin and DNA/RNA) on the knife - especially in the concentrations alleged by the prosecution ("strong smell of bleach" etc).

So the only scenario which in any way fits this study is if the knife was subjected to a highly improbable series of events: it was not only cleaned with fairly high-concentrate bleach - concentrated enough for the police officers to clearly smell, but seemingly (and inexplicably) not enough to denature DNA on the blade; it was also exposed to reducing agents (concentrated lemon juice or vinegar, or prolonged exposure to certain detergents) which affected the haemoglobin cells in their subsequent exposure to the chromiluminescence presumptive tests. Likely?

 

[LondonJohn]

No, it's a poor one because the dynamics of the two situations are greatly dissimilar. About the only commonality between the two is a heightened state of anxiety/awareness. Burglars are not in fear of immediate annihilation. Escaping prey is not hunting for items of personal value.

It's not "hunting for items of personal value" which causes fear. It's the possibility of either being spotted by a passer-by while scaling the wall/climbing through the window, or the possibility of being confronted by an unexpected occupant once inside, which causes fear: primarily a fear of being sent to prison (for the first time in this case), getting a criminal record (for the first time in this case) and suffering loss of status/support among family (although seemingly not for the first time in this case).

 

[LondonJohn]

If it was a choice between taking a bathroom break and soiling his pants, I doubt Rudy would have thought twice about finding a bathroom before he attempted entry into the house.

But what if the very act of his entry into the house caused the bowel reactions which resulted in his sudden desire to defecate....?

 

[Fiona]

Certainly LJ. It is about false negatives in presumptive blood tests. I am glad we are at least able to agree on that

 

[LondonJohn]

I stand corrected, Mr. D. I should have said "I believe," not "we know."

You are also correct that WHO's recommendations are not legally binding. They are based on concepts of medical ethics, not necessarily on national laws. Many of the indignities that were inflicted on Amanda and Raffaele were, to my mind, unethical, but not necessarily illegal.

Your objections to my post are legitimate. I need more information about this topic; some of my understanding of it may be from undocumented sources. If you have concrete information about it, I would welcome seeing it.

Also, if you agree with me in principle, what would your observations about the topic be?

Thank you!

I haven't yet seen any comments or observations regarding my post (from earlier today) about how HIV tests are actually conducted, and how false positives are astonishingly rare if a) the double test (ELISA and Western Blot) is properly conducted and b) the person being tested is not from a high-risk group. I welcome all comments and criticisms!

 

[LondonJohn]

Certainly LJ. It is about false negatives in presumptive blood tests. I am glad we are at least able to agree on that

It is indeed. We do indeed now know that false negatives to presumptive blood tests can occur a) when there has been fire damage at the crime scene, and b) when reducing agents (such as vinegar or lemon juice) have been added to the blood under examination. Thank you for bringing these special situations to our collective attention.

Under all other circumstances, a negative chromiluminescence test for blood means that a DNA test will also show negative, and therefore need not be conducted. And, unsurprisingly, the evidence in the Kercher case all falls into this "all other circumstances" bracket.

 

[Chris_Halkides]

HIV tests

I haven't yet seen any comments or observations regarding my post (from earlier today) about how HIV tests are actually conducted, and how false positives are astonishingly rare if a) the double test (ELISA and Western Blot) is properly conducted and b) the person being tested is not from a high-risk group. I welcome all comments and criticisms!

LJ,

When I looked into this issue, I came away with the impression that the first test was a false positive and the second came back negative. I agree that the second test was probably a Western blot or an ELISA and that they are less prone to false positives. Two things about this episode bothered me the most. From what I have been able to learn, Amanda was told the results of the first test but not counseled, and physicians with whom I spoke were dismayed about this. The other problem I have is that this information became public and because of a poor translation of her diary, suggested much greater sexual activity on the part of Ms. Knox than what was actually the case.

 

[Fuji]

No, it's a poor one because the dynamics of the two situations are greatly dissimilar. About the only commonality between the two is a heightened state of anxiety/awareness. Burglars are not in fear of immediate annihilation. Escaping prey is not hunting for items of personal value.

It's not "hunting for items of personal value" which causes fear. It's the possibility of either being spotted by a passer-by while scaling the wall/climbing through the window, or the possibility of being confronted by an unexpected occupant once inside, which causes fear: primarily a fear of being sent to prison (for the first time in this case), getting a criminal record (for the first time in this case) and suffering loss of status/support among family (although seemingly not for the first time in this case).

You have completely failed to grasp my argument.

Please allow me to fill in the sentences which I thought were to be implicitly understood, but now must apparently be made explicit:

No, it's a poor one because the dynamics of the two situations are greatly dissimilar. About the only commonality between the two is a heightened state of anxiety/awareness. Burglars are not in fear of immediate annihilation. By way of contrast, prey attempting to flee from a predator is in fear of immediate annihilation. Escaping prey is not hunting for items of personal value. On the other hand, it should be noted, burglars are actively engaged in a search for items of personal value.

In the comparison which you created, a burglar's state of anxiety was held to be analogous to the terror an antelope feels when chased by a lion. This is not an appropriate comparison.

As to the other likely sources of anxiety you enumerated, I am not in disagreement. That's anxiety - not terror. It should also be noted that these factors are precisely why Rudy would be quite unlikely to defecate at the scene in the first place.

 

[Mary_H]

I haven't yet seen any comments or observations regarding my post (from earlier today) about how HIV tests are actually conducted, and how false positives are astonishingly rare if a) the double test (ELISA and Western Blot) is properly conducted and b) the person being tested is not from a high-risk group. I welcome all comments and criticisms!

I would like to respond to your post, LJ, but I'm pressed for time at the moment. I will look at it tonight. Mr. D's just happened to catch my eye because it was addressed to me. More later.

 

[LondonJohn]

You have completely failed to grasp my argument.

Please allow me to fill in the sentences which I thought were to be implicitly understood, but now must apparently be made explicit:

No, it's a poor one because the dynamics of the two situations are greatly dissimilar. About the only commonality between the two is a heightened state of anxiety/awareness. Burglars are not in fear of immediate annihilation. By way of contrast, prey attempting to flee from a predator is in fear of immediate annihilation. Escaping prey is not hunting for items of personal value. On the other hand, it should be noted, burglars are actively engaged in a search for items of personal value.

In the comparison which you created, a burglar's state of anxiety was held to be analogous to the terror an antelope feels when chased by a lion. This is not an appropriate comparison.

As to the other likely sources of anxiety you enumerated, I am not in disagreement. That's anxiety - not terror. It should also be noted that these factors are precisely why Rudy would be quite unlikely to defecate at the scene in the first place.

I do indeed seem to have completely failed to grasp your argument.......

By the way, please can you refer me to the part in my argument where I compared a burglar's state of anxiety to the terror and antelope feels when chased by a lion? That analogy (read back) was to argue that these types of feelings do not necessarily significantly diminish after a number of events which elicit that fear. My quote, just to recap, was:

"Why might Guede's previous (alleged) experience of burglary greatly diminish any heightened sense of fear/anxiety during this break-and-enter? Do antelope which are being chased by lions experience any less fear on account of the herd having been chased by lions previously?"

Please could you indicate to me where I suggest that the level of fear felt by the antelope in my analogy is equivalent to the level of fear/anxiety felt by a burglar as he enters a property?

Anyway: as you say, I have completely failed to grasp your argument, so I will stop posting any more tedium on this particular subject.

 

[LondonJohn]

LJ,

When I looked into this issue, I came away with the impression that the first test was a false positive and the second came back negative. I agree that the second test was probably a Western blot or an ELISA and that they are less prone to false positives. Two things about this episode bothered me the most. From what I have been able to learn, Amanda was told the results of the first test but not counseled, and physicians with whom I spoke were dismayed about this. The other problem I have is that this information became public and because of a poor translation of her diary, suggested much greater sexual activity on the part of Ms. Knox than what was actually the case.

Indeed. Over and above any moral/ethical issues around why she was informed of a false positive in the first place, the way in which this information seemingly leaked to the media is shocking and morally bankrupt. And, incidentally, even if Knox herself (or her people) chose to release parts of her diary to the media, she had every right to keep this deeply personal part private. Do you (or anyone) know when this HIV test and AK's diarised sexual history were first reported in the media?