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pete22 comments on The Amanda Knox Test: How an Hour on the Internet Beats a Year in the Courtroom - Less Wrong

42 Post author: komponisto 13 December 2009 04:16AM

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Comment author: pete22 14 December 2009 08:52:49PM *  3 points [-]

By far the most important evidence in a murder investigation will therefore be the evidence that is the closest to the crime itself -- evidence on and around the victim, as well as details stored in the brains of people who were present during the act.

the evidence against Guédé is such that the hypothesis of her guilt is superfluous -- not needed -- in explaining the death of Meredith Kercher

I think you’re begging the question here. Those who are convinced that K&S are guilty seem to believe that the evidence from the crime scene itself suggests that Guede could not have been the only participant – i.e. his involvement does NOT completely explain the death of Meredith Kercher. They seem to believe this for two reasons:

  1. The various evidence at the crime scene itself of a clean up and/or staged break-in, things like the bra being cut off or the body being moved – hard to attribute to Guede because a. he wouldn’t have had time (is this true?), and b. little effort was taken to remove evidence against Guede himself, even very obvious things like flushing the toilet.

  2. I haven’t seen any commenters mention it here, but one of the anti-Amanda sites, in quoting the Micheli report, seemed to imply that Kercher’s injuries were inconsistent with a single attacker.

Your post appears to take for granted that these are not credible arguments, but they seem like a very significant part of the prosecution’s case – and the part that I found hardest to assess without English versions of the Micheli report and other source documents. Can you explain how you reached this level of confidence?

FWIW, I'm not an Amanda-hater …my prior probability of her guilt was 30%, and I'm ready to revise it down. I’m just not sure I fully understand your argument on this point.

Comment author: rmattbill 15 December 2009 02:55:55AM 7 points [-]

"little effort was taken to remove evidence against Guede himself, even very obvious things like flushing the toilet."

The assumption here is that Knox and Sollecito carefully removed their DNA, but did not remove Guede's. Isn't the more rational explanation for all of the evidence against Guede, and the lack of evidence against K&S, that Guede did it and K&S weren't even there, as they have always claimed, and as Guede claimed no less than 5 times?

Further, there's a lot of supposition about a "clean-up" floating around on the web, but no evidence of one. There's lot of talk about bleach, bleach receipts, bleach on the knife, etc., but no evidence was introduced to support any of these claims.

Another claim is no prints were found for Knox, therefore she must've wiped them down. This presumes, incorrectly as it turns out, that no unusable prints were found. In fact, lots of smeared, smudge, or partial prints were found. The prosecution's own expert witness on fingerprints, Giuseppe Privateri, testified he saw no sign of the place being wiped down for prints. There were lots of prints, just not a lot of usable ones, which is totally normal since the way we use our hands often causes the oils left behind to be smeared.

Also, to believe this theory of a clean-up, one has to believe that with Superman-like enhanced vision, Knox and Sollecito could see their fingerprints and DNA, and Guede's, and could selectively remove their without disturbing his. This seems far-fetched in the extreme.

In the bathroom, some of Kercher's blood was found mixed with Knox's DNA, probably from splashing onto a hair follicles or dead skin cell from Knox. Why didn't this happen in Kercher's room, where the orgy took place? No intermingling of sweat, saliva, or other bodily fluids- in an orgy?!?! It boggles the mind.

Last, a lamp from Knox's room, her only source of light, was found on the floor in Kercher's room, possibly put there by Guede as he tried to look for his possessions, or look for obvious signs. If Knox so carefully scrubbed Kercher's room she was able to eras every invisible spec of DNA, why would she leave her bedroom lamp behind?

Comment author: AnnaGilmour 15 December 2009 04:23:21PM 1 point [-]

The idea of a staged break in is unsubstantiated. There is a broken window. Mignini added the interpretation without evidence of such a thing. The two shards on top of the bed turned out to be polka dots on a piece of clothing.

Comment author: AnnaGilmour 14 December 2009 09:02:35PM *  5 points [-]

One thing to remember is that Mignini fired the coroner doing autopsy investigation when that person said it was the injuries of a single perpetrator. He then hired someone who said it was more than one perpetrator. If you would like, I can find a link to back it up. So the original report said one person caused the injuries.

Comment author: Eliezer_Yudkowsky 14 December 2009 09:16:51PM 2 points [-]

Huh. I wondered if something like this might be the case, but then wondered if I was being selectively skeptical of the prosecution and trying to dismiss all of their evidence. Next time I'll remember to (a) trust myself a little more, and (b) remember that reality itself is consistent rather than fair, i.e., Knox obviously didn't do it, thus if the coroner says it's more than one perpetrator, I should (b1) construct a model in which the coroner is pressured (or fired and redealt) and (b2) penalize the probability of that model because (hopefully) most coroners aren't pressured.

Comment author: MichaelVassar 15 December 2009 10:05:56AM 2 points [-]

I'm not sure how much hope fits into the Bayesian analysis. My impression is that doing things like pressuring coroners is routine in the US and probably in Italy as well. Of course, pressuring coroners is a special case of "doing things like pressuring coroners" and thus unlikely a-priori, but its not very unlikely a-priori and once the possibility is raised it doesn't call for much penalty.

Comment author: AnnaGilmour 15 December 2009 04:25:41PM 1 point [-]

The significant factor though is not that the coroner was fired and replaced by someone who would report multiple perpetrators. The significant factor is that the original, unprompted, unbiased, objective analysis was that it was a single perpetrator.

Comment author: pete22 15 December 2009 06:01:22PM 0 points [-]

Anna, I'd be curious to see the link on this when you get a chance.

Comment author: AnnaGilmour 15 December 2009 06:08:18PM 1 point [-]

If you type "Mignini fired coroner" into Google, a list of articles comes up. There were too many from which to choose.

Additionally, a great specific, scientific explanation and analysis on the LCN DNA gathering and testing can be found at ScienceSpheres by Mark Waterbury. He starts the blog that way. He has a PhD in materials science.

Comment author: pete22 15 December 2009 07:36:58PM 1 point [-]

I tried a Google search -- I get a few mentions of Mignini firing his coroner, but they either don't mention a reason or they say it was punishment for leaks to the press. None seem to be from impartial sources, i.e. one is from that truejustice site, another is an article in the Stranger (seattle weekly) by a friend of Amanda's ...the closest thing to a real news site was a Vanity Fair article, and like the others it doesn't mention the first coroner saying there was one assailant.

This is the problem I mentioned in another comment -- all of our info is second- or third-hand. I'm surprised at how comfortable people are citing this stuff. If this was a comparably public case in the US, there's a good chance the entire reports from both the old and new coroner would be on the Smoking Gun and we could be linking to them directly...

Comment author: AnnaGilmour 15 December 2009 09:25:32PM 0 points [-]

It was part of the trial, however, which is why people cite it.

Comment author: pete22 16 December 2009 12:20:54AM 2 points [-]

One thing to remember is that Mignini fired the coroner doing autopsy investigation when that person said it was the injuries of a single perpetrator. He then hired someone who said it was more than one perpetrator. If you would like, I can find a link to back it up. So the original report said one person caused the injuries.

Again, can you give us your source for this? I'm not doubting you, I just want to get an idea of where it comes from.

Comment author: komponisto 15 December 2009 02:37:50AM *  4 points [-]

The various evidence at the crime scene itself of a clean up and/or staged break-in, things like the bra being cut off or the body being moved

A bizarre or unexpected condition of the crime scene is not the explanandum here; Meredith's death is. One person is entirely sufficient to have killed Meredith, and the DNA evidence establishes with virtual certainty that Guede had the kind of contact with her necessary to accomplish this. Unless the evidence suggesting someone else was involved is of comparable power to the DNA evidence against Guede (something on the order of 30 bits), then (and this is the part people have trouble understanding) even paying attention to it at all is automatically hypothesis-privileging.

(EDIT: Eliezer corrects below. What I actually wanted to argue here was that, given the certainty of Guede's involvement, the lack of connection between him and Knox or Sollecito is strong evidence against their involvement -- probably enough on its own to outweigh the comparatively weak evidence against them provided by the alleged indications of multiple attackers at the crime scene.)

Yes, we might be curious about the unusual mechanics of the crime scene given only one person, but unless they are so strange that assuming someone else's guilt of murder (when we already have a suspect) would constitute a reasonable explanation for them, we have to regard the whole question as a distraction.

Comment author: Eliezer_Yudkowsky 15 December 2009 04:34:37AM 6 points [-]

Unless the evidence suggesting someone else was involved is of comparable power to the DNA evidence against Guede

Doesn't follow. You can have a lot of evidence for one true statement and then less evidence for another true statement.

Comment author: komponisto 15 December 2009 04:43:23AM *  0 points [-]

Not sure I understand the objection. The point is that the evidence is extremely weak by comparison; not strong enough to justify any attention.

Comment author: Eliezer_Yudkowsky 15 December 2009 05:53:29PM 4 points [-]

Whether evidence is strong enough to justify attention is an absolute threshold. There is no "extremely weak by comparison". There is just "extremely weak".

Comment author: AnnaGilmour 16 December 2009 12:04:03AM 1 point [-]

It is extremely weak on its own, and its weakness is compounded and confirmed by the strength of evidence of someone else. The reason for this is that the strong evidence sets up a perameter, a reference point of what is possible for evidence left behind. It puts lines on the thermeter by which to read the murcury. This is because there is also no evidence of collusion, so the physical evidence has to carry most of the weight, if not all. Otherwise, the prosecution's case operates via a tautology.

Comment author: komponisto 15 December 2009 08:58:31PM 0 points [-]

Huh? Attention isn't binary, off-or-on; like evidence itself, it's a quantifiable commodity. The stronger the evidence, the more attention. Right?

Comment author: Cyan 15 December 2009 09:23:31PM *  1 point [-]

There will be some threshold of evidence below which a hypothesis ought to receive strictly zero attention. You could probably even formalize this in terms of bounded rationality.

Comment author: komponisto 15 December 2009 09:36:54PM 1 point [-]

Right, but I don't need to claim that the anti-Knox evidence is below that threshold. Unless, that is, we're talking about extremely imperfect less-than-Bayesian human minds, who can't intuitively perceive the difference in weight that a perfect Bayesian would assign to 30-bit evidence vs. 10-bit evidence.

Comment author: pete22 15 December 2009 04:47:03AM 2 points [-]

You're right, this is the part I have trouble understanding. Partly because I have trouble separating the facts of this particular case from the theoretical point you're making. So if you'll humor me for a second: let's say you're the chief of police somewhere, and one of your detectives comes back from a murder scene and tells you "we've arrested a prime suspect and we've got very strong evidence against him, including an ironclad DNA match that ties him to the murder. but we don't think he acted alone, because of X, so we want to keep looking for another suspect."

It sounds like for almost any X, your response would be "Don't waste your time. Case closed. Your hypothesis that there was another killer is unnecessary to explain the victim's death." Is that correct? What kind of X would suffice for you to let your detectives keep investigating?

Comment author: komponisto 15 December 2009 04:54:23AM *  1 point [-]

What kind of X would suffice for you to let your detectives keep investigating?

Two examples that come to mind immediately:

-Similarly incriminating DNA from someone else in addition to the prime suspect.

-Information acquired from the prime suspect himself that points to accomplices.

Comment deleted 15 December 2009 05:02:29AM [-]
Comment author: komponisto 15 December 2009 05:13:49AM 1 point [-]

Maybe. But remember that reality is consistent: If two people were at the scene committing the crime, why would there be vastly more evidence of one than the other?

Once you have the suspect, you can interrogate him to find out who he knows.

Comment author: pete22 15 December 2009 05:11:01AM 0 points [-]

Come to think of it, why would a further (unknown) DNA sample even be enough? You've got an explanation for the crime. Surely there are far more likely priors than a double murder that would explain a second DNA sample, right? "Similarly incriminating" might not really be possible; much of what made the first sample so incriminating is that it matched a guy who you already had reason to suspect. Or did you mean that an unknown DNA sample would not suffice, only one that matched another suspect?

Comment author: komponisto 15 December 2009 05:19:00AM 0 points [-]

If the victim's body and surroundings contains DNA from two different individuals, that would suggest multiple attackers.

Comment author: pete22 15 December 2009 08:01:08PM 1 point [-]

OK, fair enough. I think I understand your standard better now. But let's go back to the actual case. Here's a quote from that truejustice site's summary of the Micheli report:

2) Judge Micheli explains that blood evidence proves that Meredith was wearing her bra when she was killed. Nor is it just the blood on her bra which demonstrates this. It’s also where the blood isn’t on her body. He says that Meredith was wearing her bra normally when she laid in the position in which she died, and she was still wearing it for quite some time after she was dead. Her bra strap marks and the position of her shoulder are imprinted in the pool of blood in that position. Meredith’s shoulder also shows the signs that she lay in that position for quite some time.

He asks the question: Who came back, cut off Meredith’s bra and moved her body some time later? It wasn’t Rudy Guede. He went home, cleaned himself up and went out on the town with his friends. Judge Micheli reasons in his report that it could only have been done by someone who knew about Meredith’s death and had an interest in arranging the scene in Meredith’s room. Seemingly who else but Amanda Knox?

She was apparently the only person in Perugia that night who could gain entry to the cottage. And the clasp which was cut with a knife when Meredith’s bra was removed was found on November 2nd when Meredith’s body was moved by the investigators. It was right under the pillow which was placed under Meredith when she was moved by someone from the position in which she died. On that clasp and its inch of fabric is the DNA of Raffaele Sollecito and Amanda Knox. Micheli reasons in his report that Raffaele and Amanda seemed to have returned to the cottage some time after Meredith was dead, cut off her bra, moved her body, and staged the scene in Meredith’s room.

At what point exactly do you part ways with Judge Micheli in that chain of reasoning? To me, his reasoning starts to sound stretched around the middle of the second paragraph. But it sounds like you might have a problem with this logic from the very beginning ...? Are you saying the evidence that the body had been moved is just not worth paying attention to?

Comment author: komponisto 15 December 2009 10:18:44PM *  1 point [-]

Are you saying the evidence that the body had been moved is just not worth paying attention to?

If, starting from the premise of Guede's involvement, there are reasons to infer the involvement of someone else, then that sort of thing may very well be worth paying attention to. If the trail through Guede goes utterly cold, however, there comes a point where you just have to declare that Guede's actions + there's-something-we're-missing-about-that-other-"evidence" is a more parsimonious explanation of the data than Guede's actions + someone-like-Amanda-Knox-is-guilty.

In this situation, we should suspect that, if we bothered to investigate further, we would find that we were missing something. And sure enough, by golly, that's what often seems to happen.

Comment author: pete22 16 December 2009 03:55:17AM *  3 points [-]

OK, but why do you keep saying "if"? The judge is making an argument on your terms. He is trying not to privilege the hypothesis. He is starting from the premise of Guede's involvement, and he does find a reason to infer the involvement of someone else. He does not conclude that the trail goes utterly cold, but instead that it leads convincingly to Raffaele and Amanda.

Now, you may disagree with this argument, but I still haven't heard the substance of your disagreement. All you've done is gainsay it.

Don't get me wrong -- I think your original post was a very good explanation of some huge conceptual problems in the way the case against K&S has come together. If I came in believing they were guilty, you would have raised massive doubts in my mind. And that's no small accomplishment on your part. But it doesn't follow that no case against them remains. In order to convince me, or anyone else who's around the average of 35%, that we should lower our odds to your 1-10% range, I think you have to address the facts more directly. It's not enough to say "there comes a point when you just have to declare..." or that certain DNA evidence "doesn't count."

If you were a defense attorney and we were jurors, then you're right, you'd have your acquittal. But it's not a juror's job to distinguish between a 1% and a 35% probability of guilt. To make that case, I don't think you can just point out weaknesses here and there in the prosecution's argument -- you need to lay out the strongest version of the prosecution's case, even if you have to put it together for them, and then show step-by-step why it doesn't lead to a probability higher than 1-10%.

I don't blame you for not doing that, because as I've been saying, the primary sources aren't available to do it -- at least not in objective, quality English translations. I'm just not sure how you can get to such low odds without taking a more granular approach. You've suggested that the correct prior is the (very low) odds of someone like Amanda committing homicide, and others have suggested that the correct prior is the (very high) odds of a convicted defendant in a modern legal system being guilty -- but these are two ends of a spectrum, not binary alternatives. Finding the correct point on that spectrum is equivalent to assessing the strength of the prosecution's case.

Comment author: komponisto 16 December 2009 07:31:12PM *  2 points [-]

He is starting from the premise of Guede's involvement

No he isn't! He's starting from the premise that some investigator found the condition of Meredith's clothing and bloodstains to be unusual given the hypothesis of only one killer. As far as I can tell, he has failed to update properly on the lack of connection between Guede and anyone else who might be a suspect -- not to mention the lack of other evidence (e.g. DNA) that would indicate two or more killers.

In order to convince me, or anyone else who's around the average of 35%, that we should lower our odds to your 1-10% range, I think you have to address the facts more directly.

I'm starting to suspect that we may just have a disagreement about how strong the anti-Knox evidence is. Yes, I agree it isn't literally zero. But that's not the point. The point is that it is utterly dwarfed by the other evidence. Exactly how strong of a dwarfing is this? Well, that's what seems to be the point of contention. I claim the net evidence of Knox's guilt yields a probability of no more than 0.1; you're uncomfortable going below 0.35. The only way to resolve this would be to do some sort of rigorous calculation of the inferential power of clothing-mechanics-analysis evidence -- something which I think would take us too far away from our main topics here.

I suppose I can console myself with the fact that it's good news for Amanda and Raffaele (and bad news for the prosecution) if what are probably the most intelligent and sophisticated discussions of their case on the whole Internet consist of vociferous arguments about whether the probability of their guilt should be 0.35, 0.1, or even lower.

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: AnnaGilmour 15 December 2009 11:57:50PM 0 points [-]

I don't believe there was a staged break-in, but even if there was, how does one logically go from "staged break-in" to Amanda staging it? I detect a logical gap.

Comment author: AnnaGilmour 16 December 2009 12:58:49AM 1 point [-]

I am new to this site. Can someone elucidate for me why the statement above might have been seen as a minus? Just curious. I was asking for the logical link between the condition of the room and Amanda. One hasn't been provided, not even by the prosecution.