The sheriff finds Pete's car with the shotgun laying on the backseat. She doesn't charge him with a crime since he has a "license". No license or permit is required to own or transport a shotgun in Iowa. However, it is illegal to transport one without it being locked in a case or disassembled.
When the group are discussing the number of people who were killed, they waiver between 9 and 10. Pete reveals a cast that shows 10 tick marks which would make the total so far 11 - because the first character killed, Zach, wasn't counted. However, up until this point, you only see that there were 8 total murders so far. A look at the credits demonstrates that other victims - an "immigrant hater" and a "skinhead" were cut from the film.
When the group is arguing after Luc stabs the woman who hates Catcher In the Rye, the victim is supposed to be dead with a knife in her back, slumped over the chair, but she can clearly be seen breathing.