For people who wouldn't have had a roommate during that time period, it would be Saya, Percival, Akira, Girge, and Andersen. Percival had said he hadn't woken up when Marty left the room, but he also could have been lying if he's a Prophet. Although like Yukina said, they could have just slept through it.

[ TIME TO WAIT... ]

Out of all of those, we've already said we want to check Girge, and I think Percival should be on our list considering he knows Yukina's role. Did Andersen say exactly where it was placed? Do you know if there's a specific range?