Just like any daughter, Kerri Rawson adored her father.

Growing up in Park City, Kansas, Rawson and her father, Dennis Rader, went on hiking trips and enjoyed fishing excursions together. He was by her side as she graduated college and walked her down the aisle on her wedding day.

He also was a cold-blooded murderer behind closed doors.

It has taken Rawson nearly 14 years to be able to come to terms with her father’s secret double life — which devastated her family.

She recalled how an FBI agent knocked on her door and told her: “Your dad is BTK,” which is an acronym depicting his preferred method of murder: Bind, Torture, Kill.

“You don’t want to believe it’s true,” Rawson said in a recent ABC 20/20 documentary which details her father’s reign of terror. “The father you know is not capable of any of this.”

Rader murdered ten people in Wichita, between 1974 and 1991, while taunting police to catch him.

He was finally arrested in 2005 after resurfacing to announce that he was preparing to kill again.

Detectives were able to trace a computer disc he sent them — with Rader’s name embedded in the disc’s metadata — to a local Lutheran church where he volunteered.

What Rawson didn’t know — she would give the police the missing piece of the puzzle they’d spent 30 years searching for — DNA evidence.

“They found out I had had annual pap smears and they got a warrant for my medical records,” Rawson stated. “It would have been nice if somebody had asked me for my DNA. I would have willingly given it.”

Rawson, now a 40-year-old married mother of two, was initially angry when she learned that the police had used her medical records. “It felt,” she says, “like an invasion of my privacy.”

But she came to understand that they didn’t have much of a choice. “They needed to catch my dad. They needed to be safe about it and needed to do it quickly,” stated Rawson.

Her father showed no emotion as he admitted to the killings in chilling detail in court.

“I had many… I called them projects. They were different people around town that I followed, watched,” he told the court. “I had never strangled anyone before so I really didn’t know how much pressure you had to put on a person or how long it would take.”

His daughter was shocked by his admissions.

“It’s insane,” Rawson said. “He says the most insane things about what he did. I knew it was coming… I had read about the crimes, but hearing about it in his own words was devastating.”

After unmasking her father as the brutal “BTK” serial killer who had terrorized her hometown of Wichita for decades, Rawson struggled to find closure.

“I had to learn how to grieve a man that was not dead, somebody I loved very much that no one else loved any more,” she explained to 20/20. “I wasn’t corresponding with BTK. I’m never corresponding with BTK. I’m talking to my father. I’m talking to the man that I lived with for 26 years…I love the man that I knew. I don’t know a psychopath.”

At the advice of a pastor at their church, she wrote her father a letter.

“Dear Dad, No matter what you may have done or not done, you are my father and I love you…” she wrote in her new memoir, A Serial Killer’s Daughter, recalling that initial note.

His response was largely unsatisfying, giving her few answers beside an admission that he had “serious problems.”

Yet she continued to write.

“I’m not forgiving him for what he did to those other families,” said Rawson. “But I am forgiving him for what he did to our family. At some point you have to let that go, you have to let the guilt — you have survivor’s guilt because you survived something and other people didn’t,” she explained.

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After pleading guilty to ten murders, Rader is now 73 and is serving 10 consecutive life sentences at the El Dorado Correctional Facility in Kansas.