Conversation so far:
who kills tree gelbman in happy death day
Tree is lured into a tunnel and murdered by a figure wearing a mask of the school mascot.
How did Lori plan Tree Gelbman's murder in Happy Death Day
Lori gives Tree Gelbman a poisoned cupcake.
Why did Lori plan Tree Gelbman's murder in Happy Death Day
Lori was also having an affair with Dr. Butler, whose preference for Tree Gelbman drove Lori mad with jealousy.

Question: Who is the masked killer
Self-contained rewrite: Who is the masked killer in Happy Death Day