Joseph James DeAngelo Jr - also known as the Golden State Killer - has admitted to the murder of 13 people in the 1970s.
The 74-year-old Vietnam veteran and former police officer said an 'inner voice' made him carry out the brutal killings.
Speaking in court this week, Sacramento County Prosecutor, Thien Ho claimed DeAngelo had made several incriminating statements while alone in an interrogation room after he was arrested in 2018.
He has never acknowledged the murders in public, but is claimed to have said: "I did all that.
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"I didn't have the strength to push him out. He made me. He went with me. It was like in my head, I mean, he's a part of me.
"I didn't want to do those things. I pushed Jerry out and had a happy life. I did all those things. I destroyed all their lives. So now I've got to pay the price."
DeAngelo managed to evade arrest for decades and was never suspected by police until he was linked to the murders via DNA evidence collected from the scenes and from his vehicle.
It is believed DeAngelo has entered guilty pleas as part of an agreement with police, with allegations also including a number of rape cases. The plea deal is thought to spare him from the death sentence.
Earlier this month, we told you about a new docuseries set to explore DeAngelo's killing spree, which landed on HBO and Sky Atlantic on 28th June.
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The true crime tells the story of writer Michelle McNamaraa, who - after writing an article about the then little-known killer for the Los Angeles magazine - signed a book deal to write a novel on the case.
It's titled I'll Be Gone in the Dark after the chilling words the killer spoke to one of his victims: "You'll be silent forever, and I'll be gone in the dark."
But tragically, Michelle sadly died in her sleep from an accidental prescription drug overdose at the age of 46, and never finished the book.
Husband Patton Oswalt made it his mission to complete the book and release it, along with crime writer, Paul Haynes and investigative journalist, Billy Jensen.
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The trailer for the series is truly chilling, with victims recalling: "We were awakened by a voice and a bright light. There was a real sense of evil in the house."
"He made me tie up my husband," another said, with her husband adding: "He ordered her to put dishes on my back."
"If I hear these dishes fall down I'm going to kill your family."
You can watch the series on HBO or Sky Atlantic now.
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