OAKLAND — After more than two years of psychiatric evaluations that deemed him mentally competent and other continuances, a 49-year-old former bartender and registered sex offender will face criminal prosecution in the killings of three women in Oakland more than 20 years ago, authorities said.

Michael Monert, who has been in custody since September 2012, is charged with three counts of murder and the special circumstance of multiple killings that happened between 1989 and 1991. Authorities believe he could be responsible for other killings.

According to authorities and court records, Monert has admitted to the killings he is charged with, providing details only the killer would know, with bludgeoning the main method of death. He believed the women were prostitutes.

The cases Monert is charged with are:

He is scheduled for a court appearance for the three killings on April 11. He is being held without bail.

Officer Herb Webber, the lead investigator in the cases, said the Sanders killing led to the other women being identified as suspected Monert victims.

Sanders was found with her head bashed in covered with debris. She was killed elsewhere and her body dumped on the street. Fingerprints were found at the scene but none could be matched at the time.

Webber took over the investigation as part of the “cold case” team in 2012.

He learned Monert’s fingerprints had been put on file after an Oregon sexual assault conviction that mandated he register as a sex offender. His prints matched those found at the scene where Sanders was found.

Monert was arrested in September 2012 in Hayward where he lived at the time and was charged with Sanders’ killing. He would not talk to police then.

After a preliminary examination he was ordered to stand trial for the killing and was being held at Santa Rita Jail.

Webber continued to sift through cold cases looking for other similar killings and in December 2013 got help from an unexpected source: Monert.

Monert told Santa Rita deputies he wanted to make a full confession to his “cases.” According to court records he talked freely to police about the killings. He said he believed all the women were prostitutes but that he never had sex with them.

He admitted killing Sanders in a San Pablo Avenue produce market where he worked at the time before dumping her on 24th Street.

He said he picked up a woman later identified as Flahiff on International Boulevard and drove her to the 2100 block of Courtland Avenue in East Oakland. He said he hit her with a hammer, pushed her body onto the street and ran over her with his truck. Autopsy records confirmed she was hit in the head and there were tire marks on her body.

The slaying of Adkins was confirmed using Oakland Tribune archives.

Authorities said Monert admitted picking up a woman later identified as Adkins on International Boulevard on the pretext of having sex and driving her to a house on Paxton Street in East Oakland where he then lived. There, he bashed her head in, leaving a pool of her blood on the floor before dumping her in the Oakland hills, authorities said.

The case was not in the Oakland homicide unit records. But a clipping about the death and where Adkins was discovered at the Roberts Park entrance was found in Tribune archives at the Hayward Area Historical Society.

East Bay Regional Park District police first handled the case but turned their investigation over to Oakland police.

The blood found on the floor of the Paxton Street house was later determined to be Adkins’, authorities said.

Monert was charged with the additional murders in January 2014 but soon after court proceedings started, they were suspended for him to be mentally evaluated. He was found to be mentally competent in 2015 but there were other continuances since then.