I'm sorry to hear about your car...I've been there. Unfortunately when you hit someone from the rear the cops call it "your fault" no matter what. But, the truck driver acted illegally by leaving the scene of an accident. He was probably drunk or had no license, etc.

I once rear-ended a trailer, being towed by a pickup. The trailer was a large box, completely concealing the truck in front. Well, the trailer didn't have any brake lights even mounted on it, so when he stopped it caught me off guard and I had no time to react. He had cut me off too, so I was already close to him when he stopped. I slammed him, and in turn he slammed a pickup in front of him. The cops conceded that his trailer was illegal, but I still got pinned with fault, he got fault for hitting the guy in front of him.