There ain't no guarantees that a guy is going to work out when you hire them. This guy was a military vet with nothing in his background to indicate that he was stupid. He killed a violator that, for what ever reason, made him angry enough to do so.
It's not like he was a commercial Air Bus pilot with an extensive history of mental problems and suicidal tendencies that flew a plane into a mountain.
He was smart enough to fool everyone his superior. Now if he knew that he would always be on film, do you think he would have lost his cool (so to speak) and so coldly killed the man.
