A serial killer has little to no emotions. They don't feel guilt or sadness, they only feel the need to kill, in most cases.

The families of the victims all have emotions towards the situation. Even people who didn't know the victim have some sort of feelings around the case.

A serial killer steals away the innocence of their victim.

The killer has no innocence left in them. It was stolen from them many years before they killed. Something traumatizing could have happened to them that took it away.

As many people know a serial killer has a different mental state than most people. They're usually born with it or its triggered by a trauma.

The victims families and the victim (if they survive) end up having a warped mental state. They can end up with depression, PTSD and so on.