How to be proven innocent against a charged with receiving stolen property?

My husband and I decided to purchase a car off of a private seller and his buddy we met through work. It was in very poor condition and ran but not very well. It had 215xxx miles and was also very dirty. The guy was asking $600 which is below the value for that car because he'd had it for a while and knew that were expecting a child within the month and needed a car. He told us his buddy lost the key and seemed genuinely sincere about it, and they even tore his buddy's whole hard and house up looking for it. They told us they can rig it so we just use a screwdriver to start it and they'd pay for a replacement key if they couldn't find it. So because they seemed sincere about having lost the key and we were in desperate need of a car, we decided to let them open the ignition up so we can just use a screwdriver to start it. We all agreed upon giving them $400 cash this week and the other $200 the following Friday. They wrote up a written contract with their names and my husband's name stating that once my husband paid the other $200 they'd sign the title over to us. They brought out the title and we didn't actually look at it but it seemed legitimate as well. So we drove off with it under that agreement and with a copy of the written contract. The next day we were driving on the freeway and got pulled over by about 6 cops and were arrested for driving a stolen vehicle. They let me go because I'm 9 months pregnant but they took my husband into custody. I was able to bail him out later that night and yesterday he had his first court appearance which they just gave him another court date. We've been told that basically the written bill of sale doesn't mean much and that there's not a lot we can do. Were from other state and are here on business and are supposed to go home this week but can't because of all of this. How can we prove his innocence and go home before my due date?