Im a Christian, isnt it wrong to kill another person?
It is wrong to murder someone else. Killing in self-defense is a different matter. In Luke 22:36, Jesus tells his Apostles: But now, he that hath a purse let him take it, and likewise his scrip, and he that hath no sword let him sell his garment, and buy one. It was expected that the Apostles would face evildoers in their journeys to spread the Word, and so Jesus advised them to defend themselves. Some would argue that failing to defend the gift of life given by God would be sinful. Your spiritual leader would be a better person to ask than me though.