I don't know the background of this case, but it IS important to distinguish between innocent people being convicted of a crime they didn't commit, and violent low-life scum being convicted of a crime they didn't commit. The latter is a lot more common than the former (as so aptly demonstrated by that monster who got sprung a couple of years ago on a "wrongly convicted" decision, and promptly abducted, raped, tortured, and killed a young woman, burned her body and hid it in a junkyard). Juries and judges generally take the defendant's demeanor, and other info about him/her into account (though they're generally not allowed to hear specifics of past convictions until the sentencing phase) when deciding if the evidence is sufficient to convict, and sufficient to warrant life w/o parole or the death penalty.
Why? Do you think the outcome of a trial should only depend on your opinion of the perp rather than whether it's the right person? You seem to be willing to commit two crimes; first convicting a person who did not do the crime; and second, letting the real perp go.
A crime is commited. A person is executed. Point made. ¡Strelnikov!