They should value their lives equally. 99 of those people are innocent of further wrong-doing and you are victimizing THEM. Using the state to do so, in fact. I'm more of a libertarian than you are. Have them serve a reasonable term for what they have done, and since I place an emphasis on rehabilitation I'm even willing to accept the idea of sentences being conditioned on a good-faith belief that they HAVE been rehabilitated, within some mild limits to protect from overextension and abuse of state power. But I cannot and will not punish someone for future crimes they MIGHT commit, anymore than I will do so for those who have not yet been caught committing a crime, i.e. the supposed innocent of yours.
There is no number because you can't apply probability to decide whether you are going to toss someone in jail for a crime they have not provably committed.