My two older stepchildren (now 18 and 22) got into a lot of trouble when they were in high school. It was always a fact that their mother or father (my husband) tended to sheild them from the real consequences of their actions. I feel that they still don't understand true consequences for their actions, but we have learned from this.
On another note, I can remember my brother breaking into a church when he was 16 and stealing all the sound & computer equipment. My parents prayed about it and had him apologize to the church and then face whatever the church decided would be the appropriate punishment. Luckily for him they made him make repairs and clean up and write an apology letter. He got off pretty easy but it scared him straight.
I don't think even your son's biological father wants to see him get in trouble, so if you two can be amicable and present a united front to your son, maybe it will make a good impression on him. You have to put the past in its place....the past and move on for your son's sake. It may be good to have a male role model especially at this time in his life (if he can be a good role model).
Still letting your son face the consequences of his actions now, while he is still a juvenile, my keep him from continuing the trend when the punishment is more harsh, as an adult. Good luck, keep praying for him. Don't give up on hope, he is still a child.