One reason I don't think FG violently killed DS, following from what appears to be LE's theory that the crime occurred in the house on Robina-Oxford:
he's still a free man
Violently kill someone in a house, and a few days later the police are there talking to you and raiding your house....blood splatter, defensive wounds, broken furniture, stained/missing carpet, hair, fibers from clothing, etc.
However, if someone OD's, there's far less of that sort of thing. Sure, a few fibers from clothing. But no blood and signs of a violent struggle (defensive wounds, broken furniture, holes in walls, etc)
Maybe the police found all of that. But I'm guessing they did not. Esp if they needed to take the cars (and maybe electronic items) in and process them before they had enough probable cause to go back for other items. Dunno if that's the case, but it's weird they didn't take what they took later right away. Assuming the initial warrant delineated certain items and they had to get those and validate their theory before going back for another warrant to take the other items.
Hence, I'm leaning OD vs he beat her to death or shot her or knifed her.
See: the Lauren Spierer case for an example of where it's likely she OD'd in an apt and the police had full access to the apt right away and were unable to come up with enough evidence to make an arrest of the people there with her that night.