After arresting serial killer Gary Hilton outside a convenience store in Georgia, police were left "anxious" after learning the body of a missing hiker was not with the suspect.
Left with the overwhelming task of finding hiker Meredith Emerson's body in the Georgia section of the Appalachians, police made "a deal with the devil."
"I went up to the jail where we were holding Hilton. I met with his lawyers. I asked them to go talk with him, and I told them that I wanted to know where Meredith Emerson was right then," former Georgia Bureau of Investigation Special Agent John Cagle said in "Blood Mountain."
"They talked to him for several hours and came out and asked me if I would call the local prosecutor to see if he would be willing to consider taking the death penalty off the table in return for the location of Meredith Emerson," he continued in Fox Nation's new limited series.
Fox Nation's two-part series "Blood Mountain" investigates the vanishing of Emerson, Hilton's arrest and his eventual confession and conviction in other murders.
Hilton was arrested on Jan. 4, 2008, after being caught cleaning out his van by a witness. Police responded to the scene within minutes and captured Hilton, who was described as looking "guilty as sin."
The arrest was made three days after Emerson went missing on Jan. 1 while hiking Blood Mountain, the highest peak on Georgia's Appalachian trail.
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"Meredith spent a lot of time outdoors," Emerson's friend, Brent Seyler, said in the Fox Nation series. "She was all about her dog, and she was all about nature. She loved being outside."
As a Colorado native, Emerson was not scared off by the advanced and hazardous hike up Blood Mountain. However, she was not prepared for the horror that awaited her in the woods.
During Hilton's confession, he revealed not only where Emerson's body was but how he killed her.
The National Forest Serial Killer, as Hilton became known, said he took Emerson deep into the woods and struck her in the head with a tire tool until she died. Hilton also said there were two crime scenes – one with her body and another a few miles away with her decapitated head.
"I'm going to tell you right now, there was never any plan to let her go," Hilton said in chilling police recordings.
Hilton pleaded guilty to Emerson's murder and was sentenced to life in prison.
After the Emerson case, Georgia officials launched a group effort with officials in North Carolina and Florida to investigate whether Hilton was involved in two other unsolved murders.
Law enforcement officers soon linked Hilton to the murder of 46-year-old Cheryl Dunlap, who was discovered in Apalachicola National Forest in Leon County, Florida.
Two years after being sentenced to death, Hilton pleaded guilty to the murders of married couple John and Irene Bryant, ages 80 and 84, respectively, who disappeared while hiking in October 2007 in North Carolina.
Hilton was sentenced to death in Dunlap's murder.
"A life for a life," Dunlap's cousin, Marsha Misso, said in Fox Nation's "Blood Mountain." "I feel like he deserved the death penalty, and I was glad he got it."
The damning evidence in all the cases came from the van Hilton had when he was arrested in 2008.
"An enormous amount of articles were in the van. A lot of evidence that had blood on it. A lot of items in the dumpster," Cagle explained during the Fox Nation series.
Hilton remains on death row in Florida.
"The national forests are great places to go to get away from just about anything you can think of," Cagle said.
"But hikers need to be aware of their surroundings," he cautioned during the Fox Nation special.
For more on the National Forest Serial Killer and the "deal with the devil," catch Fox Nation's two-part series "Blood Mountain," now streaming.
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Fox News' Stephanie Pagones contributed to this report.