Who Is "The Professor" on The Perfectionists? Breaking Down the Most Likely Suspects

Why He's the Killer:

• As Alison points out, Mason reacted strangely to Nolan's death. He went from sobbing at his funeral to trying to take his place the next day in class. Perhaps Mason was always jealous of his best friend and decides to kill him so he can have his life.
• It's eventually revealed that Mason and Claire had an affair shortly after Nolan's death. Perhaps he was working with Claire to kill him.

Why He's Not the Killer:

• While the evidence against him is a little suspicious, it almost seems a little too obvious that Mason is the killer.
• Following his affair with Mona, it's clear the he has developed true feelings for her. It seems unlikely that he would blackmail her.