If it really was a one person case (or two people, mabey) of a criminal and an innocent in a room and I had to either send both to jail or let both free, I woud let both free. As said before, the criminal can always be caught again. In the real world legal system, however, you have to accept that mistakes will happen; criminals will have evidence against them dismissed or destroyed an likewise innocent people will be "proven" guilty to a certain jury. So the real question is: how many criminals do we let free before we convict an innocent? Too many and nobody goes to jail. Too few and everybody's locked up.