Nearly every single crash I have seen that involves more than 1 vehicle is a result of somebody committing some type of traffic violation, otherwise the collision wouldn't have occurred. Also, there is almost always evidence of this to the level of probable cause. This sounds like it is the case here as well. A thorough crash investigation on scene should have resulted in a citation being issued, it definitely makes things a lot tougher for the OP when the LEO's just leave things up in the air.

Good info from a lot of posters above about contacting insurance. Best of luck Nick Papagiorgio.