> Those things all infer guilt, but don't directly prove it.

Which is why they're all so untrustworthy. Take your example: If what actually happened is that you were sitting next to your friend having a beer when a madman came in and shot your friend, and then you wrestled the gun away from the madman and barely escaped with your life, you would get all that same "evidence."

Given that there are only two kinds of evidence, circumstantial and eyewitness, and that eyewitness evidence is almost useless unless the witness knows the accused (and was close enough and had a good-enough look not to be mistaken) or the accused was apprehended in flagrante delicto, bet on circumstantial either way (to convict or to clear). Dismissing circumstantial evidence means that if you sort of resemble the impression that an eyewitness had of the perpetrator and were wearing clothes that were "brown, or maybe blue... it was kinda dark" and the testimony of that eyewitness just, you know, feels more credible than the seventeen people who will swear up and down that you were elsewhere at the time, then the more objective (but "merely circumstantial") evidence that can reliably place you elsewhere isn't going to be a whole lot of help to you.

I'm not saying that eyewitness testimony is automatically better. It's generally pretty terrible, and people have all kinds of different incentives to lie on top of being mistaken.

The underlying problem is that we're making decisions that change the course of lives based on weak evidence of any type. Nobody wants to actually follow "beyond a reasonable doubt" because it would mean too low a conviction rate, so instead we suffer too high a false conviction rate.

But you're also confusing what classifies as one type of evidence or the other. The seventeen people who swear you were somewhere else are eyewitnesses to your alibi. In addition, circumstantial evidence is extremely useful to acquit, because although proof that you could have committed the crime doesn't prove that you did, proof that you could not have committed the crime does prove that you didn't. The prosecutor has a tough job, and they're supposed to, because they're proposing to lock a citizen in a cage for a number of years. That's a thing that should happen a lot less often than it does.