IIRC, it was only that his fb messenger/chat said "active". His account did not make any posts or answer any messages. There was discussion about this that if his family had his log in info OR if he was logged in on a shared device left at home, then the messenger could show up as active even while no one was looking at it. Also I believe this was reported to the press by Olivia's sister who has never met Brian or his relatives and she heard it from mutual friends. Since the families don't know each other, his family may not have told her family if they had access to his fb to check it. Plus, LE has likely been pinging both their phones-- How would Brian access fb messenger without turning on his phone or another device and being immediately tracked by LE tracing the pings? IMO, the "active" fb messenger is a red herring.