here is a list of bible verses about forgiveness

Matthew 6:14-15
For if you forgive men when they sin against you, your heavenly Father will also forgive you. But if you do not forgive men their sins, your Father will not forgive your sins.

That is perhaps the most important principle from Jesus' ministry.

Eliza, The way I see it. You are not asked to forgive those who sin against others you are told that if you forgive those who sin against you, God will forgive you for your sins against others.   

I can't claim to know what Jesus knew 2,000 years ago, but he was a very intelligent individual. Others here have made similar points to this. Forgiving is for the forgiver. I think it is easier for a camel to roller skate across the Sahara than for an unforgiving person to have peace of mind. That's why you should forgive those who trespass against you. Even if they steal or do you violence. Don't get me wrong here. You should still aid in the prosecution. If you thought they were a danger and you wish to prevent another victim from feeling your pain you can speak against them in a parole hearing or refuse to give them a character reference. But for you be forgiven by God, you have to, in your heart, forgive the criminal.