Continuation - Discussion of the Amanda Knox case

[loverofzion]

It's a problem, isn't it?

We know it's not blood.

Nobody has any idea what it might be if it isn't blood, or why it should have survived the cleaning with bleach that the prosecution claimed occurred when absolutely no blood did.

One hypothesis is that it was just a bit of grot on the blade with no DNA in it at all, and that some of Meredith's DNA that was already present in the lab contaminated Stefanoni's test run creating the illusion that it was tissue from Meredith.

Another is that an officer who had picked up some of Meredith's skin cells at the murder house contaminated the knife when they picked it up - secondary transfer is a known phenomenon, so this too breaks no laws of physics or biology.

Another is that Stefanoni decided to mock up a good result and chucked some of Meredith's DNA into the final run since nobody from the defence was looking.

Another is that it's a chunk of skin or something from Meredith that miraculously clung to the knife after every trace of blood had been washed away with bleach. This theory is even less likely that the previous three, especially given that the knife was almost certainly sitting in its drawer in Raffaele's house when Meredith was murdered by Rudy, because at that time Amanda and Raffaele were almost certainly right there in Raffaele's house with it.

None of which theories have any sound basis in scientific fact.

 

[loverofzion]

The knife 'looked like it had been vigorously scrubbed' - not just clean, but vigorously scrubbed.

'A strong smell of bleach coming from the apartment'. How would that work, exactly, assuming the knife was 'vigorously scrubbed' on the night of the murder? Bleach has a rather pungent smell, so I often open a window after using it. That way I don't have to inhale the unpleasant odour.

Who knows WHEN the knife was vigorously scrubbed?

And perhaps RS and AK did not share your airing out habit.
That or it had been scrubbed shortly before the police swept in.

 

[loverofzion]

Actually, on the knife blade, she said it was not blood and I gave you the quote from her testimony. Did you even read my post?

I read your post and went back to the report.
Stefanoni said there was not enough blood sample to retest.

 

[loverofzion]

Kev: "If the knife was vigorously scrubbed with bleach, then there definitely wasn't any of Meredith's DNA on it."

No chance that they missed a bit, in your opinion?

And this proves---?

 

[Kevin_Lowe]

Again, read the report.
Stefanoni said there was not a sufficient sample to test for blood.

You are yet again making factual claims which are simply false. You seem to do this frequently, yet you do not acknowledge it when you are corrected.

Stefanoni tested part of the sample to see if it was blood, and the test was negative. So what was it? That's anybody's guess.

Then she stuck what was left in her DNA testing equipment and eventually coaxed a positive result for Meredith's DNA out of it.

 

[Charlie Wilkes]

___________________________

Halides,

As you mentioned earlier, Meredith's DNA was abundant in the lab. Well, since virtually all of the lab samples of Meredith's DNA would have been blood.........should we not expect that the DNA on the knife---if contaminated in the lab--- would have tested positive for blood? But it didn't. In which case, the negative test for blood should indicate that the knife was not contaminated in the lab.

///

By definition, contamination would come from a source other than the sample itself, i.e., an instrument in the lab. It happens all the time, which is why LCN is so controversial. They are also supposed to run negative controls (gel with nothing added) to see if something shows up that shouldn't be there. Did they do so in this case? If they did, they won't provide the data.

 

[Kevin_Lowe]

Again, read the report.
Stefanoni said there was not a sufficient sample to test for blood.

I think what you may be trying to say is "Stefanoni tested it for blood, and the test came back negative, so she decided that those grapes were sour and the sample was too small to test for blood anyway, so it doesn't prove anything, so there!".

 

[Withnail1969]

Who knows WHEN the knife was vigorously scrubbed?

And perhaps RS and AK did not share your airing out habit.
That or it had been scrubbed shortly before the police swept in.

Wasn't Amanda supposedly shopping for bleach early in the morning after the murder?

 

[Kevin_Lowe]

None of which theories have any sound basis in scientific fact.

It's all good. The fact that contamination is possible thanks to Stefanoni's sloppy methodology, and the lab's highly suspicious refusal to hand over the relevant documentation, mean that Stefanoni's results are not proof beyond reasonable doubt of anything.

It's not enough to secure a conviction to argue that it's just barely conceivable that it really was some tissue from Meredith on the knife blade and that it got there because she was stabbed with it. You have to prove it was tissue from Meredith, and prove it got there because she was stabbed with it. Since on balance it's far more likely it was no such thing, the prosecution would have been completely out of luck with this bit of evidence in a properly carried out trial.

Hopefully that error will be corrected in the appeals.

 

[odeed]

I'm not necessarily sure about that. Lots of things in Meredith's room or house could have had non-blood DNA from Meredith's skin cells on them. Bearing in mind this is only a speculative hypothesis, I don't think this rules it out.



I'm not aware of any rule that says that contamination occurring at the lab must have been evenly distributed amongst all the items there - it just takes one error where someone doesn't change gloves or a particle gets swept up by an air current to cause contamination, there is no requirement that someone get an aerosol can full of contaminant and hose the place down.

In addition I believe the knife sample is the only sample where Stefanoni used her unique "LCN" analysis method of cranking up the number of replications without using additional precautions to avoid contamination. So contamination that might have gone unnoticed in less-amplified samples might have been detectable in the knife sample.

Halides1 is better at this stuff than I am and will no doubt correct any errors I may have made.

Regarding the LCN testing of the knife, I was also under the impression that Stefanoni increased the amplification beyond standard to obtain the DNA results from the knife, but I seem to remember reading since that she actually increased the sample size (or number of cells) to be tested gradually until DNA protein was detected, thus the "Too low/Too low..." notes, and the knife DNA was tested using standard PCR methods.

 

[loverofzion]

You are yet again making factual claims which are simply false. You seem to do this frequently, yet you do not acknowledge it when you are corrected.

Stefanoni tested part of the sample to see if it was blood, and the test was negative. So what was it? That's anybody's guess.

Then she stuck what was left in her DNA testing equipment and eventually coaxed a positive result for Meredith's DNA out of it.

How does one "coax a positive result" in DNA testing?

I am afraid it is you who err this time.
Check back the report- as well as recent postings on- yes, PMF- and you might learn something.
You never know.

 

[Chris_Halkides]

bleach review

Kev: "If the knife was vigorously scrubbed with bleach, then there definitely wasn't any of Meredith's DNA on it."

No chance that they missed a bit, in your opinion?

The officer who once claimed that Sollecito's flat smelled of bleach later amended his testimony to say it smelled clean. But, hey, let's run with the bleach idea for a minute. We know from the journal Biotechniques that bleach is recommended for destroying DNA. We also know that Promega recommends a 33-fold dilution of bleach to clean pipets, but they also caution that one must rinse away the bleach out of the pipet, or the remainder will destroy wanted DNA. In other words a dilution of dilute bleach is still enough to destroy DNA. So if there were still traces of bleach on the knife blade (and bleach, being a liquid, can flow where it wants), there will be no DNA.

 

[LondonJohn]

Come again?
Shoe size can increase from 42 to 46 size because of a large toe??

Note the words "help to explain", as opposed to "explain". There were likely myriad reasons why Guede elected to wear size 46 shoes and Sollecito size 42. I was suggesting that one of the (many possible) reasons might have been for Guede's unusually-long second toe to be more comfortable in a larger shoe.

However, what we do know is that their actual feet were only 3mm different in size.....

 

[Chris C]

I read your post and went back to the report.
Stefanoni said there was not enough blood sample to retest.

Blood sample? The knife tested negative for blood.

 

[loverofzion]

The officer who once claimed that Sollecito's flat smelled of bleach later amended his testimony to say it smelled clean. But, hey, let's run with the bleach idea for a minute. We know from the journal Biotechniques that bleach is recommended for destroying DNA. We also know that Promega recommends a 33-fold dilution of bleach to clean pipets, but they also caution that one must rinse away the bleach out of the pipet, or the remainder will destroy wanted DNA. In other words a dilution of dilute bleach is still enough to destroy DNA. So if there were still traces of bleach on the knife blade (and bleach, being a liquid, can flow where it wants), there will be no DNA.

The DNA was found embedded ina groove; possibly the bleach did not reach in there.

What is your source for the police officer amending his testimony that the apt. smelled of bleach?

 

[RoseMontague]

I think what you may be trying to say is "Stefanoni tested it for blood, and the test came back negative, so she decided that those grapes were sour and the sample was too small to test for blood anyway, so it doesn't prove anything, so there!".

It does seem like she says one thing in her first statement and another thing in her next statement. Perhaps she is uncertain of her results.

 

[loverofzion]

Note the words "help to explain", as opposed to "explain". There were likely myriad reasons why Guede elected to wear size 46 shoes and Sollecito size 42. I was suggesting that one of the (many possible) reasons might have been for Guede's unusually-long second toe to be more comfortable in a larger shoe.

However, what we do know is that their actual feet were only 3mm different in size.....

Myriad reasons for electing to wear a certain size shoe?
What might these reasons be?

I am so glad you are only "helping to explain" and not simply explaining.

 

[loverofzion]

It's all good. The fact that contamination is possible thanks to Stefanoni's sloppy methodology, and the lab's highly suspicious refusal to hand over the relevant documentation, mean that Stefanoni's results are not proof beyond reasonable doubt of anything.

It's not enough to secure a conviction to argue that it's just barely conceivable that it really was some tissue from Meredith on the knife blade and that it got there because she was stabbed with it. You have to prove it was tissue from Meredith, and prove it got there because she was stabbed with it. Since on balance it's far more likely it was no such thing, the prosecution would have been completely out of luck with this bit of evidence in a properly carried out trial.

Hopefully that error will be corrected in the appeals.

Sorry, the conviction would have been secured even without the double DNA knife.

 

[Withnail1969]

The DNA was found embedded ina groove; possibly the bleach did not reach in there.

What is your source for the police officer amending his testimony that the apt. smelled of bleach?

Liquids flow into grooves. That's one of the properties that you might say pretty much defines liquids.

 

[Chris_Halkides]

the knife profile

Stefanoni took a portion of the sample and tested it for blood. It was negative. She took the rest and concentrated it. She also accepted a profile where 22 of 29 peaks were below 50 RFU in size, IIRC. Peaks are usually in the hundreds or thousands of RFUs in height. All of these things she did with the knife were in contrast to another sample (a possible blood stain) which apparently read that there was not enough DNA present. She discontinued testing on this sample, as she should have discontinued with the knife.