Two things:
1. Hi Chris!
B. My initial reaction is to vote for Nice Pete shooting the deer. It just makes sense. The deer needed to be shot -- it was a kindness to shoot it and as a West Virginia boy, Nice Pete would understand that.
Also, as far as I know, there are only two people with guns around. Nice Pete and Ray with Tic-Tac. That sillhouette didn't look like Ray. It looked like Nice Pete.
Finally, I don't believe that Nice Pete wanted to kill Phillippe. He really was taking him to the Super Secret Ice Cream Parlor, which turned out to be very weird in an Adaams Family kind of way and freaked Phillippe out. From what we know about Nice Pete, he kills people who (at least from his perspective) deserve it. Phillippe had done nothing wrong, so Phillippe didn't want to kill him.
Of course, now Phillippe has stolen his van. Perhaps this changes things....