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Comment author: Morendil 13 December 2009 10:47:25AM *  12 points [-]

Good points, marred by what appears at first blush like double standards. Why are you willing to selectively discount some DNA evidence while you admit other ?

You say "the supposed Sollecito DNA on Meredith's bra clasp just plain does not count" - what is that "supposed" doing in here ? The FOA site admits that the clasp was shown to carry small amounts of Sollecito's DNA.

Why does it "not count" ? Admittedly, the handling of that evidence may not have been up to the standards normally demanded by the judicial system, but why should that matter to a Bayesian analysis ? All we're interested in as Bayesians is the ratio between P(DNA on clasp|Sollecito guilty) and P(DNA on clasp|Sollecito not guilty).

The defense may well have its own convenient narratives about how Sollecito's DNA "could have been transferred to the fastener in any number of ways" owing to carelessness on the part of the police. Those narratives are just as much noise as all the other noise you've pointed to. The details of US Department of Justice guidelines for forensics are also burdensome details for the defense.

The danger of coming across as arrogant - that is, more confident than your own entanglement with the evidence justifies, not the jurors' or someone else's - is that it provides others with an excuse to abandon the hard work of thinking rationally about the case, and letting themselves be swayed by the affective components: pretty pictures of Meredith or Amanda.

What I liked about your previous post was that, without any rah-rah propaganda about rationality, you outlined a procedure for laying out our current state of (un)certainty while minimizing some of the predictable biases. There was something delightful about the implausibly level-headed discussion thread it generated. We started with an open, almost playful invitation to rationality, in a spirit of inquiry.

Here we seem to be back to a spirit of established truth and advocacy, a spirit of "getting at the teacher's answer" - we even get averaging of the students' grades. I'm expecting the discussion to be more run-of-the mill, too. (Your Postscript is also mildly insulting; if someone is smart enough to arrive at the appropriate level of uncertainty in Knox's guilt, then surely they are smart enough to figure out what to do about it.)

Here, I believe, is the bottom line. Make rationality fun, and people will play along without for a second realizing it's hard work. Make rationality sound like something people ought to have, to be as smart and righteous as you - that's a turn-off.

Comment author: Questor 16 December 2009 02:52:39AM 1 point [-]

Why are you willing to selectively discount some DNA evidence while you admit other ?

Because the 2 key pieces of evidence should be discounted because they were not arrived at by using the same type of test and were collected differently. All the other DNA testing was done using standard DNA testing in a lab that was nominally set up to do it but which did not always follow all guidelines and procedures and who did not release all data for defense experts to evaluate.

NO DNA that helped the prosecutions case was found initially on the 2 items... the bra clasp and the knife. Regular testing on the rest of the bra had strong findings for Meredith and Rudy. Amanda's DNA was on the knife handle and the bra clasp did have Meredith's as well.

Now the problem comes... the DNA specialist then attempted doing what amounts to Low Count Number (LCN) DNA test which is still experimental in most places and while now accepted in the UK it requires a very specialized expensive lab that must meet many stringent minimum requirements. The tester in this situation had never done this before, the lab was fundamentally lacking in every way to do this test and come up with verifiable, trustworthy data. And yet they did allege that they found MKs DNA or something like it... on the knife... not blood.... no blood on the knife. The DNA would have been in picogram amounts originally and easily contaminated in that lab or elsewhere by the smallest flecks of skin or dust. And there are the same problems with the bra clasp except that along with RS's alleged DNA there are 5 other peoples... unidentified. There can be little doubt that all the DNA and "all" is a very very tiny amount, much smaller than regular standard DNA can reliable even detect as being there...

Add to that no control tests were done and the "evidence" involving these 2 items evaporates. They are rightly to be judged differently from all the other DNA evidence. This looks like a DNA fishing expedition done after no DNA evidence for RS & AK turned up in MK'S bedroom. check these for details http://www.sciencespheres.com/2009/10/methods-of-polizia-pseudoscientificaa.html http://freeaman.001webs.com/pdfs/LCN_DNA_I.pdf http://freeaman.001webs.com/pdfs/LCN_DNA_II.pdf

Comment author: Jack 13 December 2009 01:05:17PM *  6 points [-]

Can anyone find statistics that could tell us what is the probability the crime scene at any given murder contains physical evidence sufficient to indicate a suspect? I would expect it to be around .8-.9 but I don't really have any idea. I'm not convinced that that probability is high enough to completely outweigh the probability that AK and RS had something to do with the crime given that

  • they knew the victim

  • are sociable 21 and 24-year-olds (one of them studying abroad) without alibis on a Saturday night

  • the probability that Guede did not act alone (which is high or low depending on how well his presence explains all the evidence at the crime scene with a prior involving the chances any given murder involves more than one perpetrator) Obviously the absence of other physical evidence is evidence that he acted alone, so this value is the probability dictated by the other evidence, rearranged crime scene, broken windows etc.

  • the facts about the morning of November 2, the non-negligible probability RS called the police after the police had arrived, the short phone calls, even the weird behavior that can be explained, which once conjoined, looks like it is at least slightly indicative of being involved in Kercher's murder.

I don't think this is actually sufficient evidence to bring the probability AK and RS are guilty over .5. But it also isn't obvious to me that this evidence is "swamped" by the lack of physical evidence implicating them.

Comment author: Questor 16 December 2009 02:29:14AM 0 points [-]

The phone timing is widely touted as some sort of proof. The postal police actually cannot establish the exact timing that is claimed. there is apparently surveillance camera footage with a time stamp that shows them still en route by car at the time RS made the call. The discrepancy is no more than a few minutes but if this is true it shows either uncertainty or something closer to tweaking facts to discredit RS. I am looking for where I originally saw this as it is actually very important to impeach the police version.

And prior to the call to the regular police RS made a call to his sister-in-law who is a policewoman. And the postal police as far as I know did not mention RS making a call after they came... or if they did it conflicts with the video of them driving there.

Comment author: pete22 15 December 2009 05:10:23AM 0 points [-]

That's setting the bar pretty high. What about witnesses who claim to have seen two men running from the scene, or heard multiple voices at the time of the murder?

Comment author: Questor 16 December 2009 02:16:55AM 1 point [-]

those would be the witnesses that appeared months later and whose testimony is doubtful. The running feet and scream women's story cannot be true... a reenactment later showed them to be impossible and they were actually not sure if it was Halloween the night before when there would have been a lot more rowdy students around... And the eyewitness was also discredited.

Comment author: Sebastian_Hagen 13 December 2009 06:41:46PM *  6 points [-]

Excellent post. I don't think I'm ready to wield those sharp implements with quite so much flourish yet; the chance of lopping off my own limbs is currently too high.

However, there are some specific parts of your post I disagree with.

You have to shut that voice out. Ruthlessly. Because it has no way of knowing. That voice is designed to assess the motivations of members of an ancestral hunter-gather band. At best, it may have the ability to distinguish the correct murderer from between 2 and 100 possibilities -- 6 or 7 bits of inferential power on the absolute best of days. That may have worked in hunter-gatherer times, before more-closely-causally-linked physical evidence could hope to be evaluated. (Or maybe not -- but at least it got the genes passed on.)

Agree completely. Now apply it both ways. Specifically:

But the prior probabilities of such scenarios are low, even in general -- to say nothing of the case of Knox and Sollecito specifically, who, tabloid press to the contrary, are known to have had utterly benign dispositions prior to these events, and no reason to want Meredith Kercher dead.

This is extremely weak evidence. If you think that psychology doesn't really matter (and I agree with that), then it notmatters in both directions. There's no obvious motive, but that's very weak evidence that no motive existed. We just don't have enough evidence for what these people really think like, relative to the population at large. Re. motive, I'd definitely stick with the prior for murderous intentions among associates.

nor, while we're at it, do the 100 picograms (about one human cell's worth) of DNA from Meredith allegedly on the tip of a knife handled by Knox, found at Sollecito's apartment after the two were already suspects [count]

I was surprised at you dismissing the knife DNA evidence. The linked FOA page claims:

Low Copy Number (LCN) tests, like the one performed on the knife blade, are regarded by many experts as inherently unreliable, because it is not possible to prevent biological contamination at the level of picograms. Even in well-run labs, control samples regularly show up with DNA that theoretically should not be there.

The actual experts doing DNA-testing in the case evidently thought that it was significant evidence. Wikipedia has an article on LCN, though a lot of the citations are broken. According to the article, the method went through an extensive review, and was finally cleared for use in the UK justice system (and with a fairly definite statement at that: "The CPS has not seen anything to suggest that any current problems exist with LCN"). The situation in some other western countries appears to be rather different, though. I still think this is fairly strong evidence, though much less so than I did before doing some research on the general acceptance of this test method.

While not particularly flattering to the defendants (how would you like to be told that there's a 35% chance you're a murderer?)

Keep in mind this verdict uses (among other pieces of information) the existing jury verdict as empirical evidence (and of course in our epistemological position, that's the right thing to do); if our judgements had been based on just the primary evidence - i.e. without an existing guilty verdict by a jury - these probabilities would have been lower.

Comment author: Questor 16 December 2009 02:07:44AM 4 points [-]

Low copy number Test... you left out that there are very few labs certified as being acceptable to do that test which is still regarded as experimental and in the UK there is a stringent set of minimum standards for equipment, procedures for the lab itself not to mention the person doing the test. Would you be surprised to hear that the lab that did the test did not meet these requirements in the slightest? It may also be true that though equipped for standard DNA tests was not technically certified at the time even for that? An expert who is convinced the results are reliable when she had never done this type of test before using equipment not designed or set up for such extreme amplification plus leaving out the other calibration tests and tests on a control and not releasing a lot of other details of what she did. She is an employee of the Italian Government just like the prosecutor who unlike many other systems also runs or in this case directs the investigation. The results on the Bra clip and the knife blade are not scientifically usable and should never have been accepted as reliable evidence. This is in the realm of pseudo science. these links have all the details http://freeaman.001webs.com/pdfs/LCN_DNA_I.pdf http://freeaman.001webs.com/pdfs/Methods_of_the_Polizia_PseudoScientifica.pdf The same with pictures and video http://www.sciencespheres.com/2009_10_01_archive.html And New Scientist Magazine has an article about concerns that world experts in DNA testing have. http://www.sciencespheres.com/2009_10_01_archive.html http://freeaman.001webs.com/pdfs/LCN_DNA_II.pdf All of this leaves 2 key bits of evidence, the only 2 alleged to link AK or RS to the crime scene... revealed to not be credible evidence at all no matter what the prosecution expert(s) said about it

This blog is great... the lead post does a good job of showing that the theory came first before any evidence and all the efforts since then have been aimed at proving the originally baseless theory which was based on pop psychology disguised as some sort of science...Dietrologia combined with a casual hunch driven version of BIA Behavioral Interview analysis. http://deception.crimepsychblog.com/?p=78 And just this short clip of Giobbi, the lead investigator at the start... is just about the best encapsulation of the mindset that originated and drove the entire wrongheaded prosecution. THEORY First , evidence after... http://www.youtube.com/watch?v=sWkZPWRS3N0&feature=PlayList&p=A24DFCC06CD8360D&index=0