Man this is something that fires me up worse than gas on a fire.
Many years ago When I had my first supra it was broken into. Funny thing about us supra owners is we have this 'daily driver' thing with another vehicle. I drove the daily to work and school. Well a guy at work approached me with my MY amps that were stolen out of my supra in Richmond. Those amps were RARE in this area and required special DIN cables. They didnt steal the DIN cables and couldnt run the amp... He was asking how to install it as there were no RCA or speaker connectors.
I had a nice calm conversation with him while my friends realized that this was my stuff and I wasnt killing this guy... I verified beyond a doubt that he and his brother had my woofers, 6X9s (cmon it was the 80s and my first real system), amps, crossovers and radar detector.
I waited a little while and went with a very trusted buddy and retrieved his vehicle... Then we deposited the vehicle in a very wet place. I know that I was a much different person all those years ago but I still stand behind the phrase "payback is a bitch".
I dont know how you can make this right and if the cops wont help you may have to go through a civil case. Things are different today and going over with a crew to whip his ass may only get you locked up.
Try the legal way first.
V