[quote=@LostDestiny]
You don’t have to kill him. You can fatally wound him and someone can come along and heal him before the wound kills him. 
[/quote]

In Peren's eyes, the man is an enemy of the king, and this elf has sworn allegiance to the king and shall protect him and his family by any means necessary.

But, perhaps.. a critical wound would be justice, the loss of a limb or perhaps his sight, surely wouldn't die quickly.