Amethyst

I hope this doesn't goes the way  I think it does go (meaning Gonta killed Miu) because that would be extremely dissapointing.

The avatar user error is basically the most ambiguous truth bullet in existance. I can pin the blame on multiple characters because of it.

"Maki, Keebo and Himiko weren't considered people because of an avatar user error. This made them non-people and allowed them pass through the wall. "

"Kokichi could have killed Miu because of the avatar user error which disables all special settings."

"Kaito could have been the killer because the avatar user error shifted his internal clock to the default setting which was used for logging out."

"Shuichi could have killed because the avatar user error allowed him to push objects because he gained debugging rights." 

What doesn't make sense is that by switching the cables you get a fully functional avatar in the virtual world (including memory) but suddenly gets memory loss after comming out. It's like switching the cables of a headphone with recording functions. It won't work.