Michael is obsessed with dates, numbers, and the Fibonacci sequence. He writes many threatening letters to Maya's mother Megan, which more or less tell his life story. In one of them, he tries to gain Megan's sympathy by describing his upbringing. Michael's father left him shortly after his birth and his mother was a prostitute. This meant he was almost always alone, feeling sorry for himself and reading at an old bookstore to pass the time.
While being interrogated, the police conclude that Michael is a "psychopath afflicted by severe schizophrenia." He shows "instances of severe loss of control, significant loss of his logical senses, a strong absence of affection, autism, and bipolar disorder." This string of psychoanalyses enrages Michael, who insists that he's not crazy.