The military would have known about his conviction, and there are operatives in the CIA and DARPA who specifically seek these types of enlisted out. The book The Men Who Stare at Goats goes into some of the apparent blackops people who were at Abu Ghraib. People with unrecognizable uniforms, no rank, who knew exactly how to push people to commit the most horrific torture.
When you look into the history of MKUltra, it's not at all outside of the possibility this guy has connections to special military operations. There's no smoking gun here of course. It could just all be coincidental. But I don't think it's outside of the realm of possibilities at all.
He was in the military from 2007 to 2010, and got convicted in 2013.
But that doesn't affect your post, since both mkultra and torture prisons guards don't get chosen out of people who did horrible crimes prior - they get stacked with dark triad personalities, who are capable of doing such things, but aren't known to have previously done so yet. They are looking for repressed sadistic feelings, and offer them a way to live them out.
I am pretty sure that anyone could tell by talking 15 min to that dude, that he is a sadist psychopath. That guy is so far gone, he will trigger all the subconscious alarm bells.
Edit:
Does anyone know who he worked for in those years between military and conviction?

