Comment author: loqi 10 December 2009 10:35:29PM *  17 points [-]

I began with zero familiarity with the case.

  1. Knox: 8%
  2. Sollecito: 10%
  3. Guede: 95%
  4. Agree with komponisto: 80%

Rationale for considering Sollecito more likely than Knox: They're linked quite closely here, but there's enough confusion surrounding the case that I can't take that completely for granted. That being the case, it's unlikely-but-possible that one of Knox or Sollecito was directly involved while the other wasn't, and my prior for a male committing a violent rape/murder is a lot higher than for a female.

Guede is clearly guilty. He fled town immediately after the murder. His DNA was found in the victim's body, by far the most difficult-to-contaminate piece of DNA evidence in the case, making it extremely likely he's the rapist. Very low prior on a rape/murder being committed by separate parties.

The inconsistencies in Knox and Sollecito's stories are definitely worth paying attention to. But there are several factors diluting their importance:

  • I already had a reasonably high prior on the prevalence of brutality and corruption in Italian police forces. This doesn't leave me with much faith in their competence, especially when it comes to interrogations.
  • It's known that Knox and Sollecito were intoxicated with alcohol and marijuana at the time. I don't know how many of you have ever been thoroughly trashed on this duo (I'm guessing the number is disproportionately low here), but memories formed under such circumstances are very fragile. I've personally experienced disagreements provoked by divergent recollections of events that had transpired an hour previously. Given that sort of influence, I know I would have a damn hard time reconstructing a coherent narrative of the night's events after the brutal murder of my roommate and several days of interrogation by Italian police.

The DNA evidence against Knox and Sollecito is also worth paying attention to, and is in fact the primary reason my estimate on their guilt is as high as it is. However, this is partially mitigated by a glaring problem with the case: Most of the evidence was collected before Guede was a suspect. If Guede had been identified from the start, the Knox-Sollecito hypothesis may not have been quite so "privileged". IIRC, the DNA of four unidentified individuals was also found on the knife. Plus the doubt wrt the knife matching the wounds. Plus the odds that Sollecito would take a murder weapon back to his apartment and put it away. My generally unfavorable prior wrt Italy's justice system also adds a fair amount of room for uncertainty here.

The fact that Guede wasn't initially identified also provides the police with a mild motive for contaminating the evidence. It's unlikely that such an action would be detected. That said, my prior for this sort of action is pretty low.

Finally, we come to the elephant in the case: The hypothesis that the murder was committed by three people working together, as the result of a sex game gone bad. This reads like a parody of a flailing prosecutor. Contrast prior with that for a "normal" rape/murder... ouch. And it just so happens that the one party implicated by actual, solid evidence is the one party who fled after the crime.

The rationale for my 80% chance of agreement with komponisto is mostly based on "metagaming" his position. He admits to having a "rather strong" opinion on the case, and it seems much, much harder to form a strong opinion in favor of guilt as opposed to innocence in this case. My estimate would be higher, but given how asymmetrical this case appears to me, I can't rule out "initial counterintuitiveness" and/or extra evidence as a possible motivation for posting this in the first place.

I'll read the other comments and post my update later today.

Comment author: Fuji 31 October 2013 11:08:59PM 0 points [-]

The facts as presented are not accurate so that is throwing off your calculation.

For example, when discounting Knox's statement to the police most people consider that it was after a length interrogation but the truth is the questioning lasted one hour. They accept that Knox was mistreated but all the evidence points to them treating her toughly but as expected for a murder suspect. What is never mentioned in the interrogation story is that Sollecito told the police Knox was not with him the night of the murder and that he lied at Knox's request. This information was in fact what led to Knox placing herself at the crime and accusing an innocent man. It should also be noted that this is the second innocent black man Knox had tried to implicate.

Also missing from consideration is the fact that Luminol revealed footprints matching both Amanda Knox and Raffaele Sollecito’s feet in the corridor between Knox’s room and the victim’s room and nowhere in the house. The prosecution advanced the theory that these were made by the accused in the victim’s blood while the defense presented the argument that these could have been made at a different time. When one of the footprints contained both Knox and victim’s DNA the expert argued independent deposit.

These are not equivalent explanations. The defense position requires that there be a reason for Knox and Sollecito to have blood on their feet. No such reason was ever given but since they had dated for less than two weeks if such an event had occurred it certainly would have been fresh in everyone’s memory. So not only does it require that there be an occurrence unrelated to the murder where these footprints were made but further both Meredith and Amanda had to deposit DNA presumably by spitting of some kind of nasal discharge in the exact same spot. We should also add a reason for why these prints only appear between the victim’s room and Knox’s room and not in the rest of the corridor. That or we accept the obvious that they were made the night of the murder in the victim’s blood.

Then there is a series of other evidence missing from the Wikipedia article. No mention of Knox lying to the police to delay the discovery of the body. No mention of Knox going from a state of joking around to hitting herself repeatedly when asked to provide her fingerprints for exclusionary purposes. No mention of Knox’s story not matching the evidence of what happened November 2. So yes if you remove all the evidence and change what you even bother to mention then Knox and Sollecito are innocent but that is not reality. If you want the real evidence I would suggest you read here http://themurderofmeredithkercher.com/ everything is sourced to primary sources and there is next to no opinion. Just the facts. See if you still feel the calculation comes out as not guilty.

Comment author: jsteinhardt 24 November 2010 03:47:17PM 1 point [-]

But, of course, the mathematics of probability theory don't work that way. A hypothesis, such as that the apparent burglary in Filomena Romanelli's room was staged -- doesn't get points for its ability to explain the data unless it does so better than its negation. And, in the absence of the assumption that Knox and Sollecito are guilty -- if we're presuming them to be innocent, as the law requires, or assigning a tiny prior probability to their guilt, as epistemic rationality requires -- this contest is rigged. The standards for "explaining well" that the fake-burglary hypothesis has to meet in order to be taken seriously are much higher than those that its negation has to meet, because of the dependence relation that exists between the fake-burglary question and the murder question.

This isn't quite true. If the prior probability of being a murderer is 1 in 10^6, and I can find 30 things that are explained twice as well by the murder hypothesis as the non-murder hypothesis, then the posterior probability of being a murderer is 99.9%, in the absence of mitigating factors (since 2^30/10^6 is about 1000.) So, many pieces of weak evidence for an unlikely proposition can still establish that proposition.

Comment author: Fuji 25 October 2013 09:48:56PM -2 points [-]

Exactly. The problem for Knox and Sollecito is that there is so much evidence that even if it was all weak (and it isn't) just the number of items is sufficent to arrive at a high certainty of guilt because they are all independent events.

http://themurderofmeredithkercher.com/The_Evidence

That is a lot of evidence. Some items are so strong that they in isolation would be sufficent to reach the level of certainty required to convict and others are strong evidence but not enough. I count 24 items.

Comment author: bogdanb 13 December 2009 09:37:34PM *  13 points [-]

I'm a bit curious about something:

If read your post correctly,* you feel that you can discount as pretty much irrelevant the opinions of quite a lot of people (jurors, police, etc), on the simple basis that people can be spectacularly wrong on occasion. (* I'm really not sure about this.)

In fact, as far as I can tell, you start from “clean” priors and do all your updating based only on the “physical evidence”; no opinions entering your calculation.

This seems almost OK, but something's nagging at me: how can you obtain thirty bits of confidence in your estimate using only evidence received from other people, via the Internet?

I'm also not sure about this, but your post seems to imply that a “good Bayesian” would be expected to assign that amount of confidence to his answer after only a couple of hours of surfing the Internet. I'm not saying that's impossible, but it really sounds very unlikely to me.

I'd very much like to see a chain of numerical reasoning that reasonably puts a 1:1000 upper-bound on the likelihood that Guédé is innocent, without starting with implicit assumptions of 100% certainty about data read from the net.* If you think an hour on the Internet is enough to reach that kind of certainty, I don't see why writing the calculations (for an upper bound, not the precise value) would take much longer, assuming that one would be gathering data and doing the calculations in one's head during that hour.

(*: EDIT for clarification. By this I mean that, for instance, given claimed evidence E in support of theory T, you don't update on the probability of T given E, but update on the probability of T given “I've read on the Internet that E”. Of course, many claims of E on the Internet have some weight, but I doubt two hours of Internet reading can add lots of weight on non-trivial subjects.)

Comment author: Fuji 25 October 2013 09:32:32PM -2 points [-]

The discounting of everyone and everything that implies guilt is the only way someone can make an argument that Knox and Sollecito are innocent. The computer shows no activity = experts are wrong. ISP shows no activity = ISP is wrong. Three different witnesses saw them = all wrong. Luminol shows footprints that match Knox and Sollecito = false positive for the Luminol. Expert says Knox shoe print in victim's room = expert wrong. Expert says Sollecito's bloody footprint in bathroom = expert is wrong. DNA = all wrong. This goes on and on.

Given the scenario of accepting that dozens of experts and witnesses are wrong or accepting that the evidence is accurate and they killed Meredith I think the logical choice is obvious.

This site has all the transcripts and is in the process of translating them into English. http://themurderofmeredithkercher.com/

It is easy to see why an hour on the internet beats a year in the courtroom is just foolish. The idea that a bunch of white knights on the internet could match a small army of experts is ludicrous