Joseph DeAngelo, the man known as the Golden State Killer, admitted 13 murders in a deal with US prosecutors designed to spare him the death penalty.
DeAngelo, who was a Californian police officer during his crimes in the 1970s and 80s, was arrested in 2018 after his DNA was found on a genealogy website.
The Sacramento hearing took place in a large university ballroom, to allow the presence of victims and families.
He also admitted several rapes, robberies and other crimes.
DeAngelo, 74, is expected to be sentenced to life in prison in August, at a second court hearing, where people injured by their crimes will be able to read the victims’ impact statements.
The sentence is expected to culminate in a criminal investigation that began in the 1970s and attracted worldwide attention.
DeAngelo’s crimes spread across the state of California and led to nicknames like Visalia Ransacker, Diamond Knot Killer, Original Night Stalker and East Area Rapist. The authorities only later realized that the crimes were the work of a man.
The former policeman, Vietnam war veteran and auto mechanic was arrested in April 2018 after the police located him, combining his DNA with a genealogy website.
Researchers created a family tree dating back to the 19th century to identify you as a suspect. Detectives followed him and collected a piece of trash he had thrown away, finding the same DNA recovered from several crime scenes.
Since then, he has been kept isolated in a Sacramento prison.
Prosecutors in the six counties where their crimes were committed agreed to hold Monday’s hearing at the Sacramento State University auditorium, which can accommodate 2,000 people, to allow social distance.
During Monday’s hearing, DeAngelo and his lawyers used plastic shields to prevent the spread of the coronavirus. He was taken to court in a wheelchair and used a cane.
Prosecutors noted that their crimes had occurred between 34 and 45 years ago and considered the geographic scope “simply impressive”.
During the hearing, he was forced to plead “guilty” for all his crimes and “I admit” for the offenses for which he had not been charged.
Sacramento County prosecutor Thien Ho said that after he was arrested in 2018 and left alone in an interrogation room, DeAngelo started talking to himself, seeming to address a person he could not control inside.
“I did it all,” said DeAngelo, according to Ho.
“I didn’t have the strength to expel him. He raised me. He went with me. It was like I thought, he is a part of me.
“I didn’t want to do these things. I pushed Jerry out and had a happy life. I did all these things. I destroyed all of their lives. So now I have to pay the price.”
However, prosecutors express skepticism about the authenticity of DeAngelo’s words and actions, noting that he feigned a heart attack after being fired from a job to shoplift.