[Laserworm]

Originally Posted by Shiro Kaisen

PLUS

Ushiromiya Battler returned to the cousins' room at 3:00 AM and fell asleep. After that, until the discovery of the crime, absolutely nothing out of the ordinary happened in the room!
In other words, it was impossible for Battler to commit murder or damage the corpses.

If we assume that an ubermensch detective with super hearing is absurd, then logically whoever Erika is was inside the cousins' room. Therefore, George could very possibly be Erika.

The red does not say why Erika knows this. It just says that it was impossible for Battler to do anything. She could be Nanjo that would make sense and it is possible that she can be Nanjo in ep6 too.