What do i have to do? To get my car back from the cops?

The cop's impounded my car because it was used as-i guess what you would call-the getaway car. I had no idea about the robbery's. Im guessing they're keeping it because its evidence, but that is my only means of transportation, and i am currently unemployed. its going to be hard to get a job, or even go to and from work. Is there a way i can petition it or something? PLEASE HELP!!!