Do you have a reasonable alternative in light of the apparent absence of the Truth Spell?
If we had access to an Omniscope that let us look back in time and view what actually happened (with multiple highly-trained people viewing and cross-checking their perceptions) we might come close to a 100% correct decision rate.
But in the absence of that, we've got to work with what we've got. In some cases, possibly many cases, what we've got is less than accurate information.
The impression I had from the trial I was on was that no one at the incident(s) was taking down notes expecting that they'd be making a deposition in a couple of years. Having an Omniscope would have cut the duration of that trial quite significantly. In fact, there'd be no need for a trial - you'd have people view the occurance and if a majority of the trained evaluators agreed on what happened, that would be all that was needed.
The current system may suck occasionally (actually that is probably undoubtedly sucks), and possibly or probably even more often than that.
What's the alternative?
Shucks, I can remember as a kid that I couldn't help looking guilty even when falsely accused of doing something.
There's going to be a margin of error in anything that is done. And that is a good reason for not rushing out and executing people, since it is far from unknown for "convicted killers" to later be exonerated.
Would it be horrible to have both innocent people in prison, and guilty people on the streets? I won't argue otherwise. I'd rather have a few more guilty people set free and fewer innocent people sent up. But if you want 100% accuracy we might as well just abolish the justice system entirely, as I don't think it is likely to happen.
cheers,
Michael