A California District Attorney has hit out at Governor Gavin Newsom's office after a decision that allows a convicted killer and rapist to walk free from prison.

San Luis Obispo County DA Dan Dow fought tooth and nail to halt the release of Alberto Tamez Jr, 75, who was jailed in 1974 to life for the murder of Genevieve Adaline Moreno.

Tamez Jr, who admitted to the crime, was given life with the possibility of parole for the slaying and rape of Moreno and was granted parole in December of last year. 

Dow's office fought his release at every turn, but Newsom's office decided to not take any further action on the decision and opted to cut him loose.

In a statement, Dow went after the governor for not opposing the release of Tamez Jr, describing the move as 'a painful outcome'.

He said: 'I am deeply troubled that our criminal and victim justice system has reached a result where the man who brutally murdered Genevieve Moreno over fifty years ago will now walk free. 

'My office fought this outcome at every stage - opposing his attempt to vacate his conviction, and making clear to the courts that Alberto Tamez, Jr. was not a peripheral figure or a legal technicality. He was the killer. He admitted it. The evidence was overwhelming.

'Genevieve Moreno deserved better. To see her killer released is a painful outcome that this office did not support and did not accept without a fight.'

Speaking to The California Post, he added: 'I think the right thing would be to stop letting violent criminals out of our prisons just to satisfy [Newsom's] policy desire to empty prisons.

'I can’t change the system he created without letting voters know how vulnerable they are by letting out dangerous criminals to empty prisons.

'I think the governor should not be letting everyone out, but he’s made no bones about it.'

Under Newsom's leadership, the state has fewer prisons due to a sharp decline in the amount of people they are imprisoning. 

Resources are instead being directed towards rehabilitation facilities, with death row in the state also in the process of being scrapped. 

According to Dow's office, Moreno was last seen working a shift at Old Blues Bar, Nipomo, in the early hours of June 18, 1974.

Her husband Richard arrived to pick her up, as was their regular custom, but he found the bar empty and the register emptied. 

Just a few hours later her body was discovered in a field a quarter mile from the bar underneath a tree. 

Investigators determined she had been robbed, kidnapped, beaten, sexually assaulted and murdered. 

Dr. Karl Kirschner, the San Luis Obispo County Medical Examiner, ruled she died as a result of being strangled to death. 

He noted that her injuries were 'classical for those of homicidal strangulation', and that he could 'think of no accident whereby such injuries and such abuse would occur on a human being other than homicide'.

Kirschner said that Moreno also suffered bruises, abrasions, and lacerations to her face, forearms, abdomen and thighs. 

The same morning Tamez Jr was identified as the sole perpetrator, with investigators finding bloodstains on his shirt and hands. 

He later admitted to hitting Moreno, robbing the bar and then dragging her to the field where he continued to beat her as she begged him not to hurt her. 

Tamez Jr pleaded no contest to the first-degree murder charge he was slapped with in September of 1974, he was jailed later that month.