Prisoners (2013) - What’s the deal with Detective Loki?

Prisoners is one of my favorite movies of all time. One aspect that keeps me going back to it is Jake Gyllenhaal’s superb portray of Detective Loki. I absolutely adore how we don’t really get to know his backstory but we understand perfectly his character traits and flaws by how he approaches the difficult case he’s assigned to.

He remains mysterious and constantly on edge but we are left with little explanation on how this young man with neck tattoos became a detective in a small town in Pennsylvania.

Do you have your own head cannon or theories about he’s background?

EDIT: Forgot to mention his facial tic that appears from the first time we see him in that diner.