The man accused of being the Golden State Killer did not enter a plea during his first court appearance.
Joseph James DeAngelo was formally charged on Friday in Sacramento County Superior Court on two counts of murder.
He was handcuffed in a wheelchair and five police officers surrounded him as he listened to the judge with his eyes barely open.
A court official read the details of the charges that DeAngelo is facing and a judge asked if he had a lawyer.
In a frail voice, DeAngelo responded: "I have a lawyer."
An attorney from the public defender's office was with him in court.
DeAngelo appeared in a wheelchair and was wearing an orange jumpsuit. He has been denied bail.
Court records also showed that investigators hunting the Golden State Killer used information from genetic websites last year that led to the wrong man.
An Oregon police officer working at the request of California investigators persuaded a judge in March 2017 to order a 73-year-old man in a nursing home to provide a DNA sample.
It is not clear if officers collected the sample and ran further tests.
The Oregon City man is in declining health and was unable to answer questions about the case.
His daughter said authorities never notified her before swabbing her father for DNA in his bed at a rehabilitation centre, but once they told her afterwards she understood and worked with them to eliminate people who conceivably could be the killer.
The case of mistaken identity was discovered as authorities hailed a novel use of DNA technology that led to the arrest of former police officer DeAngelo at his house outside Sacramento.
Critics of the investigative approach, however, warned it could jeopardise privacy rights.
DeAngelo is suspected of being the sadistic attacker who killed 13 people and raped nearly 50 women during the 1970s and 80s.
"We have the law to suggest that he is innocent until he's proven guilty and that's what I'm going to ask everyone to remember," DeAngelo's public defender Diane Howard said outside court.
"I feel like he's been tried in the press already."
Investigators were able to make the arrest this week after matching crime-scene DNA with genetic material stored in an online database by a distant relative.
They relied on a different website than they had in the Oregon search, and they did not seek a warrant for DeAngelo's DNA.
Instead, they waited for him to discard items and then swabbed the objects for DNA, which proved a conclusive match to evidence that had been preserved more than 30 years.