
Continuity mistake: In the scene where Ethan Hawke is talking through the safety glass in the barricade to the polite leader of the gang outside, the leader shoots the loud-mouth guy standing to the right of him, using the pistol in his left hand across his chest. Immediately after that they show a top shot of him dropping his right hand holding the gun. (00:46:00)
Answer: These purgers are pretty crazy. They were hunting this person, a homeless man, and they wanted to kill him specifically. They wanted their prize, the trophy of their hunt. And they won't let anyone stop them as it's their right. So being blocked from their target only increases their desire.
lionhead