SAN JOSE, Oct. 4 – He had told his parents, the police and his psychiatrist, but no one believed 34-year-old Dennis Mignano when he claimed he had killed documentary filmmaker Laurence Merrick in 1977.

Last week, the police finally began taking Mignano seriously.

“I think he was pleased that someone believed him,” his saddened father, Peter Mignano, said yesterday, two days after officers from Los Angeles and San Jose arrived at the family home to arrest Dennis.

“I think he was trying to clear his conscience.”

The slaying of the filmmaker had been a mystery. Merrick had made a documentary on the Charles Manson family, but police maintained Manson followers were not connected to the slaying.

According to his father, Mignano had attempted to share his guilt with police before last week, but his story was discounted.

This time, however, something rang true to San Jose police, who phoned their counterparts in Los Angeles. The L.A. detectives decided to arrest Mignano after he reportedly related details of the shooting that had never been made public.

Dennis Mignano has had mental problems since he was 21, his father said, moving in and out of hospitals and receiving psychiatric help.

When he took his medications, “he was as normal as anyone.” But when, as often happened, he refused medication, the younger Mignano “would have a split personality, a temper and all,” and he would ramble, almost in a trance, about his childhood and about a man in Hollywood who, he claimed “did voodoo,” his father said.

“He said this guy hurt him,” and claimed he had retaliated by killing him, Peter Mignano said.

The father said he never believed his son because: “I figured it was his imagination and because I don’t have a gun in this house.”

He said his son had no interest in the Manson family. “He didn’t like to read anything where people would get hurt.”

A frustrated tenor, Dennis Mignano may have met Merrick while trying to establish his career. Witnesses said Merrick’s assailant was a young man who earlier had picked up a brochure about a studio and acting school with which Merrick was affiliated.

Sometimes Dennis Mignano would take off, without notice, flying to Fullerton to see his aunt, Peter recalled. It may have been on one of those trips that Mignano met Merrick, the father said.

Unable to hold a job, Dennis Mignano ran 26 miles a day in a nearby park, and when he arrived home, he would “sing to himself.

“Those were the only two things he had in his life to enjoy,” his father said.

The Mignanos’ only other child, a daughter, was murdered on Niles Canyon Road in Fremont in 1977. No one has been charged in that case.

Dennis Mignano’s parents still are not certain that their son killed Merrick.

“He needs medical help,” said his father, who said Dennis had been receiving psychiatric counseling once a week. “He doesn’t belong in a jail. He needs help in a hospital.

“That’s what I’m hoping for, that he’s going to get it for a full 24 hours a day.”

By CAROL POGASH