Woman's DNA test reveals her father was a famous serial killer: 'More than I expected'

Kathy Gillcrist hadn't anticipated the DNA results she would receive when she set out to learn about her birth parents after 60 years.

The US woman, who was adopted as an infant, decided to complete a 23andMe DNA test in 2017 after retiring from working as a high school teacher.

But when the swab kit revealed she was related to someone "famous", Gillcrist learned she was possibly the daughter of one of the most wanted and notorious murderers in history.

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"In the back of my mind, I always thought that maybe I shouldn't search for birth parents because I have wonderful parents," Gillcrist told TODAY Extra.

"When I got to be 60 and I was retiring, I said let me do one of these DNA tests... I found out a whole lot more than I expected."

The test revealed Gillcrist was most likely the daughter of William Bradford Bishop Jr, who vanished in 1976 after brutally murdering his entire family with a sledgehammer.

As she Googled her possible father, Gillcrist's screen lit up with images of wanted posters and gruesome accounts of the crimes he had committed.

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"When my cousin told me I had a very famous father, she didn't tell me who he was," Gillcrist explained.

"Turns out, my birth father was a wanted criminal and performed a really heinous crime."

Gillcrist wrote auto-biography It's in My Genes about the revelation, and said she was immediately struck by her physical resemblance to Bishop and shared a number of the same health issues he encountered.

The former teacher believes her flair for the dramatic and ambition may have been derived from her father.

The New York Times reported Bishop left his office at the State Department in 1976 and beat his wife, his mother and his three sons aged five, 10 and 14, to death.

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The bodies where then driven six hours south and left to burn in a shallow grave in North Carolina, according to the FBI's reconstruction of the crime.

The abandoned, blood-soaked car was discovered hundreds of kilometres away in the Great Smoky Mountains National Park near Gatlinburg, Tennessee.

Bishop's face appeared on FBI wanted posters across the country, but has yet to be found.

Officials described him as an avid reader, expert camper and longtime insomniac who may have been receiving psychiatric care.

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Despite the gruesome crimes her possible birth father was accused of, Gillcrist said she was "pretty well adjusted" and "raised with a crazy sense of humour".

"Little did I know when I googled his name and first saw those FBI wanted posters, although he did horrible horrible things, and my heart just bleeds for his family, I had to laugh at the irony of it all," Gillcrist said.

Gillcrist attempted to compare her DNA with samples the FBI collected, but her request was denied last year.

In a statement, the FBI said that its DNA records were confidential and "restricted to criminal justice agencies for law enforcement identification purposes."