Sci-Fi: Probability of Guilt

[Sage_Rat]

Modern law seems to (generally) fall under two headings, proof beyond reasonable doubt (criminal) or the preponderance of the evidence (civil).

Basically, these are statements of probability. But they’re not actually categorized as such. The “preponderance of evidence” doesn’t mean that your odds of guilt are better than even. It means that the odds of guilt are high enough for the jury to feel comfortable letting the judge sentence you. Proof beyond a reasonable doubt, similarly, more or less means the same thing, it’s just pointed out that the penalties are higher and hence the probability of guilt needs to be higher.

But, going into sentencing, there is no correlation to the strength of the evidence. A murder serves a murderers sentence, regardless of whether there’s two unreliable witnesses saying he did it or whether there’s videotape of him commiting the act, his fingerprints on the murder weapon, clear motive, and so on. Yes, perhaps the judge can give lighter or graver sentences based on his view of the strength of the evidence, but that’s not real scientific is it? And of course, there is no way to say, “Okay you probably did it, but not enough so that we feel comfortable giving you the minimum sentence.” It’s very binary.

But so that you know that a person was killed in a room. You know that suspect A was in that room. You can estimate that it is unlikely for there to have been more than five people who could have gone into that room when the murder took place. So, the odds of his guilt is 1 in 5. Is that enough to do anything at all? No, probably not. But now say that he has a motive. What are the odds that anyone else would have a motive for killing the victim? As a fairly likeable person, let’s guess that it’s 1 in 20. Overall, there’s only 1 chance in 100 that anyone else could be our murderer. Personally, I would say that’s worth something in the way of sentencing, even if it’s only community service.

But then say that we have a second case where there’s videotape of the crime being performed. What are the odds that someone else would have blackmailed the suspect into this act? Well say that it’s 1 in 10,000. How many people would have a motive? 1 in 20, which he did. How many people would know that the victim would be in that place at that time? Up to 5 people might have known, of which our guy is one. Here we’re looking at odds of 1 in 1,000,000. Is there really enough ambiguity in that to be worth fearing the death penalty?

So let’s say that instead of juries deciding guilt or innocence, their job is simply to look at each item of evidence and decide how likely it makes it that the person is the guilty party. If it’s less than X at the end, then the person goes free. Otherwise, it’s used as a multiplier on the sentencing.

[Wesley_Clark]

If anything, weaker evidence tends to lead to stronger penalties. The reason is that when a crime is committed and the evidence is strong a suspect will either cooperate against co-defendants or he/she will plea bargain. Someone who is accused of a crime where evidence is very circumstantial will not cooperate and will go to trial, and the judge will punish them with a stricter sentence than they would’ve gotten with a plea agreement.

If anything, strong evidence against you makes you more likely to be treated with leniency because it opens the door for cooperating with investigators and prosecutors.

[Sage_Rat]

@Wesley_Clark

If anything, weaker evidence tends to lead to stronger penalties. The reason is that when a crime is committed and the evidence is strong a suspect will either cooperate against co-defendants or he/she will plea bargain. Someone who is accused of a crime where evidence is very circumstantial will not cooperate and will go to trial, and the judge will punish them with a stricter sentence than they would’ve gotten with a plea agreement.

If anything, strong evidence against you makes you more likely to be treated with leniency because it opens the door for cooperating with investigators and prosecutors.

That seems more a boon to saving money than something which punishes the guilty and frees the innocent. I’m not sure whether that’s really a strong argument for our current system.

[villa]

@Sage_Rat

Modern law seems to (generally) fall under two headings, proof beyond reasonable doubt (criminal) or the preponderance of the evidence (civil).

Basically, these are statements of probability. But they’re not actually categorized as such. The “preponderance of evidence” doesn’t mean that your odds of guilt are better than even. It means that the odds of guilt are high enough for the jury to feel comfortable letting the judge sentence you.

Actually, preponderance of evidence is usually explained in terms of probability. The standard jury instruction I have seen used is as follows…

“Preponderance of the evidence” simply means an amount of evidence that is enough to persuade you that the Plaintiff’s claim is more likely true than not true.

You also left off clear and convincing evidence, used in civil trials too. A model instruction is as follows:

Clear and convincing evidence is evidence that produces an abiding conviction that the truth of a factual contention is highly probable.

[Sage_Rat]

@villa

You also left off clear and convincing evidence, used in civil trials too. A model instruction is as follows:

I noticed it on the Wikipedia. Having never seen it referenced before, it didn’t seem worth making any further note of than in adding the “(generally)” to the OP.

[villa]

The problem is, Sage Rat, that this paragraph…

Basically, these are statements of probability. But they’re not actually categorized as such. The “preponderance of evidence” doesn’t mean that your odds of guilt are better than even. It means that the odds of guilt are high enough for the jury to feel comfortable letting the judge sentence you. Proof beyond a reasonable doubt, similarly, more or less means the same thing, it’s just pointed out that the penalties are higher and hence the probability of guilt needs to be higher.

… is just wrong.

Preponderance of evidence doesn’t refer to guilt or innocence. It is often explained in terms of a set of scales (civil plaintiffs love this one) and that if there is even a scintilla of evidence more suggesting that there is liability than that there isn’t, the jury should find liability. It is the classic >50% standard. It isn’t about “the jury feeling comfortable letting the judge sentence you.” it is explained to them as more than 50% likelihood the defendant is liable, based on the evidence.

And Proof beyond Reasonable Doubt doesn’t mean more or less the same thing. It is a MUCH higher standard. There isn’t a probability put on it because they really can’t be. Clear and Convincing evidence is the sort of civil version of PBRD. But it really isn’t the same. “Highly probable” and “beyond reasonable doubt” aren’t the same thing at all.

[Sage_Rat]

@villa

The problem is, Sage Rat, that this paragraph…

… is just wrong.

Eh, technicalities versus practicalities.

If you were correct then I should be able to look at the evidence that theoretically calculates to 50% odds, apply guesstimated odds, and arrive at a 1 in 2 figure. I highly highly doubt that to be the case. My example of a low-probability case was already in the 100s, for example.

[villa]

Conflating civil and criminal law doesn’t help. As I mentioned, in civil law Clear & Convincing and Preponderance of Evidence are directly explained to the jury in probability terms. I’ve never dealt with criminal jury instructions (Bricker would be in a far better position to comment on them than me) but it seems to me that Beyond Reasonable Doubt doesn’t break down into probability in the same way. Which seems to make sense, as depriving someone of life or liberty is considered more serious than civil restitution, which really isn’t often times about assigning blame, more about putting people back into the position they would have been absent someone else’s actions.

The reason sentencing works like it does is that guilt is a binary thing in our system. You are either guilty or not guilty after the trial. It isn’t about chances of being guilty. Hence once you get to sentencing, there is no longer in teh eyes of the system a chance whether you did it or not - you did it. Therefore what should be considered for your sentence is the severity of the crime, along with other factors.

Where the ‘probability’ comes in is earlier. I may feel very confident you killed the victim, but less confident you had malice aforethought. If the prosecutor gives me the option, I may well vote to convict on a count of manslaughter, and acquit on the charge of murder.