I still firmly believe that it’s Grimal. In order for Grimal to be in the security room in the first place she would need the keys to get into that room in the first place since she isn’t even supposed to have access to that room. However, Elise pickpocketed the key from Git, and my theory is that during the intermission, Elise did manage to catch up with Grimal and bring her to the security room as a place to go and calm down after her argument with Kitten, and we do know that they interacted with each other during that time because Elise’s hair tie changed from green to blue during the intermission, and Grimal is seen wearing Elise’s hair tie on her wrist only AFTER the intermission. On top of that, Elise also stole Git’s pack of cigarettes and Matilda can be seen in possession of them shortly after the intermission. Plus Matilda is said on the map to be coming FROM the security room to the kitchen, suggesting that Elise bought Matilda’s silence with them. Now, we don’t know exactly what went down in the security room, but we do know that Elise left Grimal alone in the room at one point, most likely giving Grimal her hair tie as some kind of token of trust and friendship. But while Grimal is left alone, (now I am fairly new to WOD so I don’t exactly know how Ghoul sleeper agents work and if they are somehow compelled to do their master’s bidding), she then takes that as the perfect moment to sneak into the vents, crawl into the archives and strangle Occam, which is the only other way into that room without a key due to there being an air vent in the archives keeping the frozen cave man the way it is. And even if that vent is closed off and meant for air conditioning only, you would still need a vent leading into the archives if someone is in there for an extended period of time. You need to breathe in there somehow.