I am a FIRM believer in NOT letting your enemies live if they are dangerous and WILL kill you when they get the chance. This guy already got away once, if I'm reading the story correctly. How they let him live after this is beyond me. They have got to realize that he is NO LONGER a member of the class and has transmuted to sub-human. Sure, they could say that they'll leave him on the island when they escape ... but I guess they don't care what he would do to the NEXT set of people.
TLDR, goodie two-shoes that don't TAKE OUT clearly identified enemies who WILL come back to haunt you piss me off.