Bruno and No-First-Name Trask act VERY guilty and conspiratorial about the murder of Dameon, the ghost is harassing them, they're both losing it as a result, heavily implying that they did it together. I don't think it's ever stated flat out.
who was Dameon? Unless someone picked up anything more than I did, he was one of many in a crowd of friends and hangers-on of Angelique's, who must all have been lovers, especially since Dameon's referred to as a "playboy".
Quentin is strangely rage-free regarding Dameon. He sees the ghost, and thinking it's living Dameon just dropping by again, he doesn't act like he does with Bruno. It's more like he was a respected houseguest. Maybe Quentin was naive about these hangers-on, not getting that they were all there for sex.
Don Briscoe left DS some time before this, for health reasons. Then his associate Larry Chase took over for Chris Collins as their lawyer. Yaeger killed Larry.