The man identified as the gunman who killed a rookie police officer in California before killing himself left a note in his apartment, complaining the Davis Police Department had hit him with "ultrasonic waves" meant to prevent dogs from barking, the San Francisco Chronicle reported.

>> Read more trending news

Kevin Douglas Limbaugh, 48, shot and killed Davis police Officer Natalie Corona, 22, while she was investigating a traffic accident Thursday night. Corona had been sworn in as a police officer two weeks before her death.

Limbaugh was found dead several hours after the shooting in a house after a standoff with police. Limbaugh died from what appeared to be a self-inflicted gunshot wound, KOVR reported.

Saturday, police released a one-paragraph letter they said was written by Limbaugh, the Sacramento Bee reported. Davis police spokesman Lt. Paul Doroshov told reporters that the paper was found face up on the bed of the gunman in his apartment.

According to Doroshov, the letter reads:

“The Davis Police department has been hitting me with ultra sonic waves meant to keep dogs from barking. I notified the press, internal affairs, and even the FBI about it. I am highly sensitive to its affect (sic) on my inner ear. I did my best to appease them, but they have continued for years and I can’t live this way anymore.”

The letter was signed "Citizen Kevin Limbaugh," the Bee reported.

Doroshov told reporters there is no way to determine when Limbaugh's note was written, the Chronicle reported.

“There have been a lot of rumors as to why this happened, why he did what he did, and we’re hoping this sheds some light,” Doroshov said.

Limbaugh had been arrested in September on a felony charge of battery with serious bodily injury, the Chronicle reported, citing Yolo County Superior Court records.

Limbaugh pleaded no contest in a plea deal, and the charge was reduced to a misdemeanor in October. He spent eight days in jail, the newspaper reported.

Corona was the first Davis police officer killed in the line of duty since Douglas Cantrill was gunned down Sept. 7, 1959, the Bee reported.

A memorial service for Corona is expected to be held in about 10 days, Davis police spokeswoman Amy Juarez told the Chronicle.