Rob, Michele and Nick were at a party together. Nick was behaving like a mad man - rude, obnoxious, confrontational. He argued with his father.
They left. Rob and Michele had concerns about Nick's behaviour. They went home. Nick stayed in the guest house at times. He preferred at-home treatment rather than attend a treatment centre.
Rob and Michele are at home. It's the end of the day. It's a large house. Nick enters the house. Given the confrontation earlier in the evening, it's most likely that Rob went to see who was entering the house, find out what Nick wanted, check his frame of mind.
Nick murdered his parents before midnight - and there's no reason to assume that he fled the house immediately after the murders. There's no reason to assume that his parents were in bed or asleep when Nick entered their house.
"Law-enforcement sources have said they believe
Nick killed Rob and Michelle between leaving the party and arriving at the hotel.
...
Security-camera footage then showed him leaving his parents’ house just before midnight, and he was spotted again a short time later
calming buying a drink at a nearby gas station."
Nick would have strolled past the hotel lobby’s quaint Christmas tree, upscale restaurant and cozy fire-pit sitting area featuring wicker chairs to get to the check-in desk to rent a $300-a-n…
nypost.com