The most logical assumption I can make is this:
hatmoza is the serial killer.
Or hatmoza is Kratos.
It makes perfect sense.
He pretends to be the psychiatrist because his role is explained as a serial killer that can be cured as a psychiatrist.
He is acting very suspiciously as well, mark of an anti-town person.
He killed off Kantor to stop the suspicion towards him.
Then he covers it up by saying Kantor helped him.
And he felt the need to bolster his credibility as said.
Vote: hatmoza
Kimi wa ne tashika ni ano toki watashi no soba ni ita
Itsudatte itsudatte itsudatte
Sugu yoko de waratteita
Nakushitemo torimodosu kimi wo
I will never leave you