- Louis was picking up Francis, so impossible to be the culprit
- Zoey was looking to the right at the time of the explosion
- Bill appears to be looking to the left, so suicide ruled out
- Francis appears to be shooting his pistol, and can do so even while being picked up. Likely conclusion is one of Francis' stray shots hit the Gas Station leading to Bill's demise.
Moral of the Story: Don't give a pistol to somebody who screams like a little girl during a zombie apocalypse.
I vote this one of the top scariest moments, I jumped. Even though I knew something was going to come for me and I hide ahead of time. And for those of you who say "Pssh this isn't that scary..." You had to be there T_T