A gunman who fatally shot his father and then a man camping at an Oregon beach earlier this week left behind notes that said he was mentally ill and planned to "kill a bunch of other people" and then himself.

Zachary Brimhall's first note says he had been mentally ill his entire life, and he had reached the point of deciding to kill himself or to kill others and then himself.

He wrote: "I chose the latter."

Brimhall, 32, drove to a beach where he shot five cars in a parking lot, killing a Michigan camper who was asleep. Later Tuesday, his father was found dead on a remote logging road in southwest Oregon. He had been shot at least eight times the night before.

The messages were contained in a notebook found in Brimhall's car, where authorities also discovered 10 firearms, more than 1,000 rounds of ammunition, firecrackers known as seal bombs and the makings for an improvised explosive device. Coos County District Attorney R. Paul Frasier released the notes Friday.

In the second note, the gunman says he is writing about three hours after the death of his father, Ray Brimhall.

"If I could go back in time, I would have driven off a cliff instead and tried to make it look like an accident to make it easier on my parents," he said. "I can't go back in time though. My life ended as soon as I fired the first round. This is not wanted. Unfortunately, there's no reason not to try and kill at least a few more people before I shoot myself."

The notes do not explain why the unemployed Brimhall wanted to kill his father or strangers. His mother, Patricia, told investigators her son did not have a drug or alcohol problem, and she never saw anything to suggest he would want to kill his father.

But the mother said her son might have been depressed at times. She said Zachary Brimhall had never taken medication for depression or been under the care of a mental health professional.

"Mom said that Zachary was a bit of a loner, didn't have many friends, if any," Frasier said Friday. "(He) never had a girlfriend as far as she knew."

Brimhall, who had a concealed weapons permit, enjoyed firearms, as did his father. The family had a picnic that included target shooting on the day of the slaying, Frasier said.

Later that night, Brimhall called his father from the Coast Range to say his car had broken down. When Ray Brimhall arrived to help, he was shot in the head and chest with handguns. Frasier said the car was fine and the call was placed to lure his father to the site.

The son then drove to Bastendorff Beach near Coos Bay, where he opened fire on multiple parked vehicles, killing David Jesse Hortman, 43, of Walker, Michigan, as he slept in his car during a tour of the coast.

Hortman's car was struck 18 times, and the bullet that hit him was fired from an AK-SAR-1, a military-style rifle. Though people were sleeping in other vehicles hit by gunfire, nobody else was hurt.

Brimhall shot himself in the head with a .44 Magnum revolver as police arrived.

Inside his car, authorities found handguns, rifles, a shotgun and the ammunition — all of which was legally purchased by Brimhall or his father.

Brimhall, whose sister died in 2008, acknowledged that his actions will cause even more pain for his mother and others.

"Sorry for all the heartache I have caused, but honestly, I really don't give a (expletive)," he said. "Knowing that I am half away from no longer suffering is the first time in my life where I ever felt completely free."

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Follow Steven DuBois at twitter.com/pdxdub