Months following the publication of a true-crime book detailing the death of an 8-year-old Pennsylvania girl, police made an arrest in the case, nearly 50 years later.

As CrimeOnline previously reported, David Zandstra, 83, was arrested in Georgia last month and charged with murdering Gretchen Harrington in Delaware County in 1975.

Fox News Digital reports that Joanna Sullivan, a Marple Township native who co-authored “Marple’s Gretchen Harrington Tragedy,” alongside childhood friend Mike Mathis, said the book significantly contributed to Zandstra’s arrest.

She added that local police directly acknowledged that they believed the book aided in solving the case.

“The book was published, and we started hearing a couple of months later that they were actively looking at a suspect. And lo and behold, it was someone she knew,” Sullivan told Fox News Digital.

Zandstra, a family friend of the Harringtons, was the pastor of Trinity Christian Reformed Church when Gretchen vanished. He helped search for her and presided over her funder when her body was found, sources said.

Police said Gretchen was last seen leaving home on August 15 walking to Bible Day Camp. Her father watched as she headed up the road. When out of her father’s view, Zandstra invited her into his car, prosecutors said.

Years later, Sullivan interviewed Zandstra for the book, released in October 2022. He didn’t remember much, but Sullivan assumed it was because it had been so long.

“I was running a Volkswagen bus with a certain amount of children to bring them to the church building, and when I got there, I think one of the teachers from Gretchen’s class asked me if I had seen Gretchen,” Zandstra said in an interview with Sullivan .”She said, ‘I thought Gretchen might be with you,’ and I said no. She said, ‘She’s not here.'”

At the time of her disappearance, Zandstra was responsible for transporting the day campers to the church in his Rambler station wagon or in a Volkswagen bus, according to the DA’s office.

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Earlier this year, a friend of Zandstra’s daughter, named in the complaint, reported waking up to Zandstra “groping” her during a sleepover at his home when she was 10. The DA’s office stated that when the friend told the defendant’s daughter, she learned this was not unusual behavior for him and that he “did that sometimes.”

Then, following the release of Sullivan’s book, someone came forward and told investigators that her classmate was nearly kidnapped twice in 1975. The informant reportedly said she thought Zandstra was the culprit and handed over a 1975 journal she kept.

Two months after her disappearance, police found Gretchen’s remains in Ridley Creek State Park.

Court documents indicated that Zandstra took the victim to a secluded area and performed sexual acts in front of her, then beat her to death when she refused to take off her clothes.

“He killed this poor 8-year-old girl he knew and who trusted him and then he acted as if he was a family friend not only during her burial and funeral but for years,” Delaware County District Attorney Jack Stollsteimer said.

Zandstra continued to work as a pastor in Georgia and Texas over the decades since the murder. He had retired and was living in Marietta, Georgia, at the time of his arrest. He’s now behind bars at Cobb County jail without bail, and fighting extradition to Pennsylvania, WXIA reports.

Investigators said they are looking into other cases for his potential involvement.

Check back for updates.

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[Featured image: Gretchen Harrington/handout and David Zandstra/Cobb County Sheriff’s Office]

Additional reporting by KC Wildmoon