Guess! Mystery

Disclaimer: Cover is a temporary placeholder, I'm still working on the official one. So, whoever put up the picture of the broken clock, do not come and say I did not give you credit because it is simply temporary.
(Rated T for language and violence)
"Hello there.
This is a mystery.
I can rewind time.
I can kill people who find out who I killed.
I can kill you.
Anytime."
In this warped world where a time-controlling murderer exists, serial killings continue happening for more than five years in gruesome or simple deaths all poised to look like suicides but definitely homicides.
This murderer has never been caught and is definitely still alive.
If he can rewind time, he can rewind time back to when he was still young and kill people.
He kills big company owners.
He kills housewives.
He kills children.
He kills businessmen.
He kills everyone.
He will kill everyone.
Who will stop it?
Someone who isn't 'everyone'.
What isn't everyone?
What isn't what everyone is?
What isn't 'human'?
Simple.
Someone who isn't considered a 'human'.