they are humans, like you, like me. they have reasons for what they do, if you were to be in there shoes you might do the same. we are all people trying to live our lives, shaped by experience. you don't stop to ask: why did he kill them, what drove him to. and instead of looking for a solution to the cause, you'd put a band aid over it by just killing them, who's acting like a dog now
So, you think that the reason for torturing innocent people can justify saving their life? I should remind you that by innocent that means they have done nothing to that person. If the guy killed his dad because his dad had tortured him then I would agree with you his actions are justifiable. However, the OP asked about people killing innocents in particular; which is the point I am arguing from.
I have given this much thought and have not been presented with any reason why someone who maliciously kills innocents should have their own life preserved. Do you feel that we are just above that? Or that they deserve a second chance to be rehabilitated? So far I have just heard put them away forever, what does that do other than waste resources?