Eliezer_Yudkowsky 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: 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.