The discovery special you mentioned showed how there wasn't a clear shot from the front; the bullet would have had to have gone through the car's front windshield. Clearly that's not what happened. Furthermore, bullets can leave quite a tail splash in their wake, throwing a wider spray of material out the entrance (JFK's skull, for instance):
Note, of course, that the bulk of the material passes through the exit. According to Newton's laws of motion, this should cause an equal force to be exerted in the opposite direction - the backwards lurch.
