Obviously there are many aspects -- the fact he had been wrongly imprisoned, the psychological toll that might take on a man, the difference between pre-meditated murder of the serial killer or whether it was just second degree murder.
Question after the cut.
My question is: what would happen to him? Obviously vigilante justice is illegal, but would there be extenuating circumstances due to the previous prison term? Is there any hope for escaping a new prison term? Parole? Perhaps a mental institution? Are there any examples of this? (Highly unlikely, I know.)
If nobody knows the answer (because there's no previous examples to draw from) then I'm interested in what would happen if you killed a serial killer without any of the other prison term stuff. Just in general terms, so I have some basis in fact to draw inspiration from.
Searched: "murdering a serial killer" "kill a serial killer" and similar permeations.
Setting: Chicago, Illinois