i think that death is the same thing as pre-life. can you remember anything before you were born? no. did it hurt? to your knowledge, no. i don't think it's a big deal, then, to be afraid of death, since just like before we were all born, we had no concept of time or pain or happiness or anything because we didn't exist. it's tough to wrap one's mind around, and i have trouble with it too, but i think it's pure logic that death equates pre-birth.
plus, about the killing spree question, i'm an athiest, but i don't kill people because i know it's wrong. it's wrong to take the life of another human being, regardless of what kind of afterlife (or lack thereof) that you believe in. actually, i find that certain religious individuals (coughgeorgewbushcough) have no problems with killing, so i can only say the question about morality and killing sprees doesn't simply apply to those who believe in no afterlife.