Wow, Erika's character development is remarkable. She went from intellectual rapist to actual rapist.
Jokes aside, I think I figured out the closed room.
There was a huge hint this chapter between Ronove, Virgilia, and Gaap. Gaap says "Escaping alone from [the closed room] is impossible." That is to say, the trick is possible with two people. Battler is trapped in a logic error, because anyone who can actually come to help him is dead or sealed, thus the number of people is now down to one: Battler himself.
However, that's wrong and misleading, because there are actually two people in the room, not one: Battler and Erika.
With Erika as the culprit, once Battler leaves, Erika sets the chain herself. She is the one who broke the duct tape seal on her own, and is also the one who killed 5 people. Since she is no longer a detective, she qualifies as one of 18 people who can commit the crime. Afaik, this also doesn't violate any red truths either.
Why Erika would set the chain herself doesn't have to be explained since this is the same logic used to trap Natsuhi last game.
