DNA evidence linked Miller to the 1992 killing of 22-year-old Angela Brosso and the 1993 killing of 17-year-old Melanie Bernas. Evidence at both crime scenes also indicated attempted sexual assault, authorities said.

Miller pleaded not guilty to the charges. Superior Court Judge Suzanne Cohen said in her ruling that Miller “claimed inability to remember the charged offenses.”

Cohen has not decided whether to prohibit Miller from claiming he was insane when the crimes occurred during the trial. The judge and two court-appointed mental health experts decided besides Miller’s alleged lack of memory about the charges, the “defendant presently has a rational understanding of the charges against him and the nature of the proceedings,” Cohen wrote in the ruling.

In November 1992, authorities found Brosso naked and decapitated in a field near the Arizona Canal north of Phoenix. Bernas’ body was found floating in the canal 10 months afterward.

Authorities found semen evidence at both crime scenes that a genealogist linked to Miller over 20 years later.

Another expert who was working with Miller’s defense team couldn’t rule out the possibility that he was faking a mental disorder, the judge wrote.

A prosecutor has characterized Miller’s insanity defense bid as a delay tactic, saying Miller’s lawyers didn’t bring up such a defense until six years after the case was filed.

In a court filing in September, Miller’s attorneys denied trying to delay their client’s trial and said another expert working with the defense team will offer an opinion that Miller has dissociative amnesia, a mental disorder in which a person can’t remember traumatic events.

In an evaluation conducted by a defense expert, Miller denied having amnesia and appeared annoyed by the suggestion that he may have dissociative amnesia. The expert conceded Miller might be been faking amnesia, the judge wrote.

R.J. Parker, one of Miller’s attorneys, didn’t return phone messages seeking comment on the mental fitness ruling.

Police said Miller denied any involvement in the killings but acknowledged living in the vicinity at the time and said he rode his bike on bike paths in the area.

Miller has maintained he is innocent and pleaded not guilty to charges of murder, kidnapping and attempted sexual assault. Prosecutors are seeking the death penalty.

After the discovery of Bernas and Brosso’s bodies, the killings faded from public attention because police were unable to link the DNA profile collected from the scenes to a specific suspect. The Phoenix Police Department’s cold-case unit was on the cases again in 2011, according to court records.

In 2014, a genealogist who uses ancestry databases in her research was given access to the DNA gathered in the investigations and eventually came up with the last name Miller. Bryan Miller had been on the police department’s list of investigative leads in the case, according to court records.

Authorities have said Miller was charged with but ultimately acquitted in the 2002 stabbing of a woman in Everett, Washington, after saying the woman tried to rob him.

The Washington state case didn’t require him to submit a DNA sample because he was acquitted. He later moved back to Arizona.

The Associated Press contributed to this report.