Was Chiaki the Mastermind?

A mastermind Chihiro AU in which Chihiro and Chiaki are both the masterminds of the killing game and, as Chihiro's boyfriend (gender neutral term needed) Leon was spared, but trapped in a room with broken limbs.

How was Chiaki the traitor?

In Chapter 5 of Danganronpa 2, it's revealed that Chiaki is an AI created by Alter Ego alongside Usami as the Observer of the Neo World Program. She revealed her identity as the traitor of the group in the fifth trial to save the students from being executed for voting the wrong culprit.

Is Chiaki the killer?

Chiaki was revealed to have been the culprit in the fifth chapter. ... They voted for Chiaki relying on Nagito's luck, and it was revealed that she was the true murderer, even though Nagito was trying to keep the traitor alive as they were not influenced by despair.