Methinks that since at the end of 1970PT Quentin reveals that he [spoiler]never loved Angelique in the first place, but was trapped in the relationship by her[/spoiler] that Dameon Edwards was an affair that Angelique had, one of her many apparently. Since Dameon was Quentin's best friend, it's my guess that he knew FOR SURE that he and Angelique were fooling around, while with all the others he probably only had a suspicion and not hard evidence, i.e. seeing them together, or being told directly from the horses mouth. So, in order to keep Quentin quiet and to keep him with her, Angelique had Bruno and Trask kill Edwards so that she would just deny the story and Quentin couldn't file for divorce because he wouldn't be able to guilt Dameon into admitting what had happened.
This is all just pure speculation on my part.