Robert Browne claims to be one of the country's most notorious serial killers. He has been behind bars for 13 years for the murder of Black Forest teenager Heather Church.

Some of the startling details surrounding his claim to killing 48 others are now spelled out in a recently released book, “Hello Charlie” by Charlie Hess. It’s a new account, written by the man who helped get a killer to confess.

Hess started corresponding with Robert Browne on a gut feeling that the 1991 murder in Black Forest wasn't the only one. That's when the confessions of a serial killer began.

On September 18, 1991, a search began for missing 13-year-old Heather Dawn Church was last seen in her Black Forest home.

The search turned up nothing.

Two years later, Heather's skull was found off of Rampart Range Road. El Paso County Sheriff's detectives would eventually link her murder to Robert Browne, a man who lived just a mile from Heather's home.

"There was only one piece of evidence against him. It was one fingerprint on the screen," said Hess.

At first, he denied his involvement to investigators. Two months later, though, Robert Browne pled guilty to Heather Church's murder. It would turn out to be just the beginning.

After 5 years behind bars, in a voluntary letter to investigators, Browne wrote a cryptic poem, “The score is: you, one, the other team, 48.”

Eventually, that letter prompted three former cops, who were all volunteering at the El Paso County Sheriff's Office to start corresponding with Browne behind bars. "I wrote Robert a letter, told him who I was and where I worked," Hess told 11 News.

That note from Hess began a four-year-long relationship. “He was writing to my home to build rapport and trust."

"Little by little, he gave us more." When the two met face to face, Browne would eventually lay out his claims to a killing spree that stretched over 30 years and nine states. They were details not made public until Hess' book.

"He had decapitated her and cut off her legs," Hess said Browne told him. That murder, Hess later connected to a young girl killed in Colorado Springs, Rocio Sperry.

"’Robert,’ I said, ‘What if the gates were to open right now, what would happen?’ He said, ‘It would be a lot worse.’"

Hess said Browne could come across as charming. He never knew the names of the people he murdered, but he could describe the spots where he dumped the bodies.

"Most of the time, it was wim-wam. He would do whatever he had to do and be on his way," said Hess.

Hess’ ability to get Browne to confess earned him a Medal of Merit from the sheriff's office and unlocked the door to new, stunning revelations from the killer. Browne claimed to have killed 49 times. If it's true, it would make him one of the most prolific mass murderers in America; the one who apparently got away with it for decades.

"When I sign books for people, I usually put on there, 'know your neighbor.'"

So far, just seven of Robert Browne's 49 murder claims have been corroborated by investigators, including the kidnapping and killing of Heather Church.

Her murder, according Browne, was his last. It was the one that got him caught, got him locked up, and stopped the spree.

El Paso County Sheriff's detectives said they still communicate with the killer behind bars, hoping to find out if any more of Browne's dozens of claims are really true.

If Heather Church were still alive, she would've celebrated her 30th birthday Monday, July 7.