Airline Captain doesn't mean he didn't have that inside him to do an evil act, just like cops doing bad things or teachers, doctors, electricians... If you catch my drift, profession doesn't really depict who someone really is or what they are capable of, imo.
Speaking from a personal experience, I was out camping in the bush at a national park here in Australia and was threatened with being shot and killed all because after being kept up all night by 4 other campers I gently let them know the next morning that there is a 10pm rule for noise, and that if rules are being broken you can be reported to the ranger and to next time be more mindful of other campers, they were up all night yelling laughing, being obnoxiously loud until 7am, less than 10 meters from my camp on a Tuesday night, I'm just glad I didn't get up during the night to let them know how much they were disturbing the peace ALL night and disregarding the basic rules because who knows what would of happened that night if I had of, we also don't know if GL had any dependencies, police weren't able to test him because he destroyed the crime scene and didn't own up. He might have been completely sober, but he may not have been, we all know how certain substances alone or combined with others can make people more enraged or irrational.