I remember an interview with one of the people from “The Innocence Project”, which works to free prisoners based on DNA evidence, which typically wasn’t available at the time of the crime and conviction. He said something which was really rather chilling.
They found that about one third of the prisoners who asked for their help in getting blood evidence retested turned out to be innocent. The other two thirds either supported the conviction, or provided no meaningful evidence. But the real chiller was what he said about all the OTHER criminal convictions, without blood evidence. There is no reason to believe that the rate of false convictions in other crimes is any different from the cases the Project involves itself in. And in fact there is a good possibility that the rate of false convictions is even higher in cases where there was no biologic evidence available.
These assumptions cannot really be proved, but the logic is pretty unassailable. Amid the prejudices and competences of judges, juries and attorneys, the actual truth of the matter is very often lost.
Which is why I decided that if I’m ever charged with a serious crime, I will sell my soul to get the very best lawyer possible. Really good lawyers get even the guilty people off.