abstractapplic's Shortform

abstractapplic

I recently watched (the 1997 movie version of) Twelve Angry Men, and found it fascinating from a Bayesian / confusion-noticing perspective.

My (spoilery) notes (cw death, suspicion, violence etc):

The existence of other knives of the same kind as the murder weapon is almost perfectly useless as evidence. The fact that the knife used was identical to the one the accused owned, and was used to kill so close to when the defendant's knife (supposedly) went missing, is still too much of a coincidence to ignore. The only way it would realistically be a different knife is if someone was actively trying to frame the defendant, and arranged for his knife to be lost at the same time; and if they could do both of those things, it makes more sense for Hypothetical Secret Mastermind X to just stab the victim with the accused's actual knife. (This means Juror 8's illegal purchase of an identical knife in the name of justice was epistemically pointless, and only served to muddy the waters; I'm oddly enamored by the probably-accidental pro-Lawful-Good thematic implications.)
The old man's testimony is suspect for more reasons than the jurors notice. The lack of fingerprints on the murder weapon suggests the culprit wiped it off first, but the old man claims the culprit ran off immediately after the body hit the floor. However, this aligns with the other reason to consider him unreliable, which is him (allegedly) managing to move quickly enough to see the accused leave the scene; it seems pretty plausible that he got the timing wrong but everything else right.
The paramedic juror's claim that the knife was used incorrectly - that it's the kind of knife made to stab up through the gut instead of down through the ribs - doesn't exonerate the defendant, and might actually incriminate him. It's a fact about the knife, not the user; if anything, a young man might be more likely than the average assailant to wield his weapon wrong.
The other witness turning out to (probably) habitually wear glasses doesn't necessarily make her testimony invalid. She could be farsighted, could need reading glasses, or could just habitually wear them to seem intelligent or as a fashion statement. All of these explanations seem more likely than a - by all accounts, scarily competent - prosecutor putting her on the stand without checking she could actually see the murder. (None of the jurors consider requesting additional testimony on this topic, even though it's both easy to check and the point which ends up deciding the final verdict.)

From all the above, I conclude:

The accused is very likely to have committed the murder.

and

The protagonist probably has some kind of agenda: either he takes issue with capital punishment, knows the defendant personally, strongly dislikes the carceral justice system, is being bribed, or is trying to arrange acquittal for a guilty party just to see if he can.

However

I still think a case can be made for the existence of reasonable doubt.

if and only if

You consider the possibility it was a suicide.

(trigger warning for detailed discussion of that thing I just mentioned)

If I knew for a fact the defendant was innocent, most of my probability mass would be on some variation of the following sequence of events.

The 'victim' has his (injury-free) altercation with the accused. This rattles the accused to the point that he forgets to take his knife with him when he leaves for the movies; he falsely assumes that it "fell out of his pocket".
The 'victim' is also rattled, and decides to commit suicide. (Possible motivations: realizing that he can no longer reliably win a fight against the target of his abuse and wanting to quit while he's ahead, feeling regret about his treatment of the accused, being angry at the accused and wanting to die in such a way that the accused ends up accused.)
The 'victim' stabs himself in the chest, and not through the gut, in an attempt to end his life as quickly, painlessly, and dramatically as possible. Possibly he shouts "I'm going to kill you!" as he does this, either out of genuine self-loathing or an attempt to implicate the accused; possibly he makes a point of staggering around near an open window with a knife sticking out of his chest before collapsing; alternatively, the witness testimonies may just be mistaken and/or falsified for reasons discussed in the film.
The accused returns home to find a dead body and two policemen. Between the lingering effects of earlier events, the presence of the victim's corpse, his current predicament and (quite plausibly) some mind-altering substances he chooses not to admit to using in the subsequent trial . . . the accused finds himself unable to provide satisfactory answers when the police ask for the titles and lead actors of the movies he watched. (He may or may not be able to recall other details about these movies: but either he doesn't think to volunteer this information and the police don't ask for it, or the police choose not to record inconvenient facts in an attempt to close the case cleanly while technically telling the truth.)

This hypothesis makes sense of the paramedic's claim about the type of knife, makes sense of the silent evidence of neither the accused nor the corpse having any injuries mentioned aside from the single stab wound (a person comfortable with violence yells an explicit verbal warning at another person comfortable with violence, and then stabs him to death, but there's no sign of a struggle?), and is supported by base rates (suicide is significantly more common than homicide in first-world nations).

. . . to be clear, I'd still say murder is much more likely, but I consider the above possibility just possible enough to be conflicted about the reasonableness of reasonable doubt in this case.

I'm curious what other LW users think.

abstractapplic2y40

4abstractapplic2y

One last, even more speculative thought:

3Davin2y

Mostly here because I was active a long time ago, but this is interesting enough to make an account again. If I use language that doesn't fit the lingo, that's why. So you know if you want to bother reading-My conclusion is that I'm pretty sure you're wrong in ways that are fun and useful to discuss! First off, it's absolutely relevant that the accused's knife isn't unique. If the knife it unique it selects for them specifically out of the suspect pool of everyone-it's not perfect evidence, it's possible that they lost it, but in most worlds where it's a unique knife they're the one who uses it on someone. Following that, and this is contextual to the story and setting, the prior probability of someone owning a knife in his community (New York young man from a vaguely Hispanic community) is high. If the specific knife is thus common enough that it's possible to find a copy within a block or so, the chance that any suspect would have access to that knife becomes pretty reasonable. I'd vaguely estimate we're supposed to estimate a greater than 90% probably that any kid of his ethnicity and gender owns a knife, and at that point we're looking at hundreds of suspects who we know could have committed the crime with a perfect copy of the murder weapon because we know one was within walking distance. We know at least two of those knives existed near the murder, so let's spitball that the chance of anyone else using that knife is about equal to the chance of the suspect using the knife. 50-50. It's much more likely that the suspect had his knife than anyone else, but there are so many other people who could have committed the crime that I don't feel comfortable saying he's much more likely than everyone. (In reality the ownership rate of knives was likely lower among Hispanic teens in 1950's America, the media exaggerated it, but people might borrow murder weapons, so we're into speculation land). Second, the flaws in the eyewitness testimony are sufficient to basical

abstractapplic2y20

Thanks for your reply, and (re-)welcome to LW!

My conclusion is that I'm pretty sure you're wrong in ways that are fun and useful to discuss!

I hope so! Let's discuss.

(Jsyk you can spoiler possible spoilers on Desktop using ">!" at the start of paragraphs, in case you want to make sure no LWers are spoiled on the contents of a most-of-a-century-old play.)

Regarding the witnesses:

I agree - emphatically! - that eyewitness testimony is a lot less reliable than most people believe. I mostly only brought the witnesses up in my discussion because I thought the j... (read more)

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