FL Debates #1: Gun Control

[goigle!]

Keep in mind if he's leaving after you gave him your wallet and you shoot him in the back, you didn't shoot him in self defense and could face felony homicide charges.

Yeah shooting him probably isn't the best idea depending on where you live.
He is still committing a crime by possessing a weapon (even if he previously legally possessed the weapon, he is considered to be illegally possessing a weapon now). I don't know if that counts as a forcible felony or not but if it does then you are within your right to shoot him, but it's iffy. It's probably just best to call the police after that.