DAVIS (CBS13) — It’s hard to miss what the community has been doing to remember Officer Corona. There have been flowers and balloons left in her honor.

As for the shooter, many are wondering what the letter he left behind says about his state of mind.

“I have never met with him so I can’t truly diagnose him,” says Dr. Diane Powell, a clinical psychologist, “But it’s consistent with a diagnosis of schizophrenia.”

Dr. Powell has worked in this field for about 55 years.

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She says this letter from the gunman shows signs of someone suffering from a psychotic disorder. In this case, she says schizophrenia, a disorder of thinking that involves delusions of paranoia.

The type-written letter, with the signature line “Citizen Kevin Limbaugh,“ offers some insight into his mindset.

It reads in part, “The Davis Police Department has been hitting me with ultrasonic waves – meant to keep dogs from barking.”

The gunman goes on to say he can no longer live with it.

Powell says his delusion of persecution by the Davis Police Department and his comment about ultra-sonic waves show that he may have suffered from hallucinations.

“He’s probably experiencing a sensory experience,” says Dr. Powell. “Something that nobody else could agree is happening. Also, there’s a hint here that he suffered long term. He doesn’t want to go on living this way any longer.”