Time to nip it in the bud.  Start with a verbal warning and taking away of privileges.  The third time you call the police - this will scare him and ask the officer to keep him in the holding cell - he must be alone - no adults or other people, so that he can learn from the enormity of the situation.  There is nothing like tough love to set him straight.  Ask the officer to talk to him first and then if he does it again then the officer can take him down to the station.

You have to take everything he has away from him and tell him that can't happen.

I think one of the answers about calling the police to scare him is a great idea.  I would also take something that is really important to him, or maybe something he thinks he can't live without.  Take it from him and make him give it to whomever he stole from.  Sometimes by example or putting yourself in the other persons shoes gets the point across.  The fact that you care, and are going to put a consequence in place is great.  I would definitely have your husband involved if not already.  Maybe he needs his dad to give more attention, or be around more.  For his age it is so important for his dad to be an example and spend quality time with him.  As his parent you know him better than a therapist.  There are many different possibilities to look at.  Is he wanting attention since he is the oldest.  The kids he hangs around with at school.  You could also teach him scripture about stealing and pray for whatever is the underlying problem. I don't think a therapist is the answer.  He needs his mom and dad.

The link below is a great tool.