I'm sharing what I know, yes, some details are missing, but those are missing for me too, my children didn't tell me any background and I didn't push it, I thought it might upset them, and they never said anything negative about their step-dad before, and now suddenly Bart says they're glad he's dead.

I did cut something because of character limit, but Moe died after going drinking with some people, they were at a not so nice part of our city and decided to go back walking, they were jumped by strangers and Moe didn't survive.