Cary Stayner confessed to the killings of Carole Sund and her teenager daughter, Juli, along with family friend Silvina Pelosso and Joie Ruth Armstrong

A serial killer who butchered four women in Yosemite National Park confessed after an FBI agent bonded with him over how the murderer's younger brother had been kidnapped as a kid and held as a sex slave for seven years, it has been revealed.

Cary Stayner confessed to the killings of Carole Sund and her teenager daughter, Juli, along with family friend Silvina Pelosso and Joie Ruth Armstrong.

He was sentenced to death in 2002 and remains on death row in California.

Jeffrey Rinek, the retired FBI agent who convinced Stayner to confess, has now written a book giving an insight into the troubled killer and his childhood which saw his brother abducted by a pedophile and held captive as a sex slave for seven years.

In Rinek's 'In the Name of the Children: An FBI Agent's Relentless Pursuit of the Nation's Worst Predators' he tells how during a 90-minute with Stayner they became 'friends' and how by building up a bond with the killer he would go on to confess to murdering the women.

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Stayner confessed to his crimes after speaking with FBI agent Jeffrey Rinek (pictured) during a 90-minute car ride

Stayner was working as a handyman at a motel just outside the California park when Carole, Juli and Silvina came to stay

The trio were reported missing on Valentine's Day and Carole's burnt out car was finally found on March 19. Carole and Silvina Pelosso's (left) bodies were found inside the trunk. Joie Ruth Armstrong's (right) decapitated body was found in July 1999 close to Yosemite

Stayner was working as a handyman at a motel just outside Yosemite National Park in California when Carole, Juli and Silvina came to stay in 1999.

The trio were reported missing on Valentine's Day and Carole's burnt out car was finally found on March 19 that year roughly 80 miles from where the women had been staying.

Carole and Silvina's bodies were found in the car's trunk and were so burnt that they had to be identified with dental records.

The cover of Rinek's book is seen above

Officers were then sent a note that gave them the location of Juli's body.

Joie Ruth Armstrong's decapitated body was found in July 1999 close to Yosemite.

Witnesses reported seeing a blue car parked outside the cabin where the Yosemite Institute naturalist had been staying, making the now 55-year-old Stayner a prime suspect.

Rinek had been assigned to the case of the women but was dropped when it seemed that it wasn't moving forward. Once Stayner was named as a suspect, he was brought back on.

Rinek tells in his book how Stayner confessed to his crimes during a car ride in the agent's two-door Thunderbird.

'I was with my wife, Lori, when I got a call to go and pick up Cary Stayner,' Rinek explained to the Mirror.

'I wasn't provided with any further information or what we were doing other than to go to a nudist colony in Laguna Del Sol and pick him up.

'The only thing I knew about him was that in 1973 his brother, Steven, had been abducted and held for seven years by sex offenders.'

Stayner's younger brother, Kevin, was abducted by pedophile Kenneth Parnell and held as a sex slave. Parnell even changed the boy's name, enrolled him in schools and pretended he was the boy's father.

Officers were sent a note (above) that gave them the location of Juli's body

The pedophile would let Steven drink alcohol and allowed one of his female partners to rape the boy when he was nine. Steven - who was 200 miles from home - grew courage to flee once Parnell returned home with a five-year-old boy.

Steven was hailed a hero for saving the boy and Parnell was arrested. Tragically Steven died in a motorbike crash at the age of 24.

And his brother's disappearance deeply affected Cary Stayner, who emotionally shared the impact with the federal agent.

Stayner's younger brother, Kevin, was abducted by pedophile Kenneth Parnell and made a sex slave for seven years. Parnell would even change the boy's name, enroll him in schools and pretend he was the boy's father

'I asked him about his brother because I worked abducted children I wanted to know what we in law enforcement could do to be better for the families,' Rinek said.

'He became very emotional when he was talking about the idea of closure when something like the loss of a brother happens.'

Rinek shared that Stayner also informed him that he had been a victim of child abuse when he was younger.

Stayner felt so open sharing his story with the agent while they waited to get through traffic on the way to the police station.

Steven - who was 200 miles from home - grew courage to flee once Parnell returned home with a five-year-old boy

'Our drive should have been 45 minutes but it turned out to be 90 minutes because there was construction work and during that time Cary and I got to know each other as friends,' Rinek added.

His brother's disappearance deeply affected Cary Stayner (pictured in 1980 hugging his mother on the day his brother was found), who emotionally shared the impact with the federal agent

They spoke on Stayner's love for Yosemite, something Rinek's wife also shares as she worked as a fish and wildlife biologist.

But Rinek still didn't understand why Stayner was being brought in to speak with law enforcement.

He said: 'The special agent in charge was there and he told us that Cary was a witness and that he was scared.

'I later found out at the trial that he knew Cary was a killer. We didn't know what to interview him about so we called for a polygraph. I'd taken takeaway orders to be delivered to the office while we waited for the polygraph to turn up.

'Both the pizza and the polygraph turned up at the same time and one of my colleagues told me Cary wanted to skip the polygraph and wanted to speak to me first.'

And when they went to go speak to Stayner, he admitted that 'there were days when he had wonderful thoughts and days where he felt he could kill the whole world'.

A note written to the agent for his great work finding lost children

'He said he had been abused as a child and wasn't able to have normal relationships with a girl,' the officer explained.

'He told me he could give me closure on what we were there about. I thought he meant he knew something more about the death of Joie.'

Agents interviewed him for six hours where he confessed to the killings and then declared that Rinek was the reason he was confessing. After confessing, Rinek promised to help contact his loved ones.

'I drove up through the night to see them and I spent several hours with them and tried to prepare them for the reality that they would be losing their second son,' he said.

Stayner was sentenced to death in 2002 and remains on death row in California.

Stayner took officers to Yosemite and helped them locate evidence of the murders. He had spent months studying true crime television and learning how not to be caught.

He pleaded not guilty to the murders and claimed insanity but that was rejected and he was convicted on four counts of first degree murder. He is currently on death row at the San Quentin Penitentiary in California.

'It was very emotional when he talked about what he had done,' Rinek added.

He pleaded not guilty to the murders and claimed insanity but that was rejected and he was convicted on four counts of first degree murder

'It's my opinion he is a person seeking intimacy with another person. He had issues in his childhood that caused problems with him and turned him into something in this life that lead him to kill.

'Most serial killers are sexually orientated. They will have a sexual fantasy and they know it's criminal.

'Most control themselves and don't go over the line.

'It has been said that he'd prepared for everything except for me.'