Nah, its implied hewas cannibalistic
This is what the characters of DR2 did:
Mikan: took Junko's ovaries
Kuyruzu - replaced his eye with hers
Nagito - the hand
Akane - starved herself
Soda - mass murderer (shown in DR2 with an automatic weapon)
Sonia - gave her parents to be experimented on
Teruteru - cooked up people
Mioda - mass suicide influenced by her music
I don't know about Nidai, Gundham or Mahiru though. We didn't get clues for them.
Wow ok what? What did I miss