The enduring mystery of why young people joined Charles Manson's murderous family appeared to be at the heart of Gov. Jerry Brown's decision Friday to reverse a parole board's recommendation and keep Bruce Davis in prison.

Brown said he wants Davis, who has been behind bars for 42 years, to come clean about all the details of his involvement with Manson's cult and the two gruesome killings of a stuntman and a musician.

It was the second time in less than three years that a California governor has rejected a parole board ruling in Davis' case. Gov. Arnold Schwarzenegger refused his release in 2010, citing the heinous nature of Davis' crimes and his efforts to minimize his involvement.

Brown repeated those reasons in a six-page decision but added his belief that Davis still has more to disclose about the killings.

"Until Davis can acknowledge and explain why he actively championed the Family's interests and shed more light on the nature of his involvement, I am not prepared to release him," Brown said.

"After 42 years of incarceration, it is encouraging that Davis is beginning to reveal the actual details of what happened. But it is clear that he continues to withhold information about these events," Brown said.

The state parole board, citing the prisoner's positive progress, approved release of the 70-year-old Davis, but the Democratic governor had the last word.

Brown gave his decision to The Associated Press at the downtown Los Angeles County courthouse after a meeting with District Attorney Jackie Lacey, who had recommended that Davis not be paroled.

Davis' attorney, Michael Beckman, called the governor's decision "horrible" and contrary to the findings of parole commissioners who conducted hearings for Davis and found him eminently suitable for parole. He said Davis has told everything he knows.

"I have represented over 700 life prisoners and of all of them, Bruce Davis is the most rehabilitated and qualified," the attorney said.

He said Brown's "paper review" of the case was insufficient to understand who Davis is today.

Brown said, "I find the evidence ... shows why he currently poses a danger to society if released from prison. Therefore, I reverse the decision to parole Mr. Davis."

But Beckman said that the governor failed to articulate any reason why Davis might pose a danger now.

If the problem is association with the Manson family, Beckman said, "They should pass a law saying if you were involved with these people you can't get out. But there is no such law. "

Brown's decision focused on Davis' role in the murderous Manson Family in the late 1960s.

"The record indicates that Davis fully embraced and championed the family's distorted values and goals, and was willing to protect the family's interests at all costs," the decision said.

Davis would have been only the second Manson-related murder defendant to be granted parole since the killing spree began in 1969.

Davis was not involved in the notorious Sharon Tate-LaBianca killings but was convicted with Manson and others in the murders of musician Gary Hinman and stuntman ranch hand Donald "Shorty" Shea.

Manson was a direct participant in both killings, according to witnesses.

Steve Grogan, another participant in those murders, was released in 1985 after he led police to where the bodies were buried in the San Fernando Valley.

Beckman noted that Grogan, a central figure in the killings, has lived as an upstanding citizen for 27 years with no problems since his release.

Davis was 30 when he was sentenced to life in prison in 1972 in the case, which was a postscript to Manson's notorious reign as leader of the murderous communal cult.

Davis long maintained that he was a bystander in the killing of the two men. But in recent years, he has acknowledged his shared responsibility. He said his presence may have emboldened others to take action because he was an elder of the group.

Brown said Davis' refusal to fully acknowledge his responsibility for the killings was central to his decision.

"I do not believe that Davis was just a reluctant follower who passively went along with the violence," he said. "Davis was older, more experienced, he knew what the Manson Family was capable of, and he knowingly and willingly took part in these crimes."

Davis became a born-again Christian in prison and ministered to other inmates, married a woman he met through the prison ministry, and has a grown daughter. The couple recently divorced.

Davis also earned a master's degree and a doctorate in philosophy of religion.

Brown commended him for his self-help efforts but said the work was outweighed by other factors.

Manson and three of his followers, Leslie Van Houten, Patricia Krenwinkel and Charles "Tex" Watson, remain in prison for life in the Tate killings. Their co-defendant, Susan Atkins, died of cancer behind bars in 2009.