Just months after the release of a true-crime book about the disappearance and murder of an 8-year-old Pennsylvania girl, police cracked the nearly 50-year-old cold case.

Pennsylvania authorities arrested and charged retired pastor David Zandstra, 83, of Marietta, Georgia, in July, 48 years after he allegedly kidnapped, assaulted and killed Gretchen Harrington while she was on her way to Bible vacation school in Marple Township, according to the Delaware County District Attorney’s Office.

Joanna Sullivan, who grew up in Marple Township and co-wrote “Marple’s Gretchen Harrington Tragedy” with her childhood friend Mike Mathis, told Fox News Digital that the book “definitely” played a role in Zandstra’s arrest, adding that local authorities personally shared their belief that the book helped them investigate and eventually close 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, now editor-in-chief of the Baltimore Business Journal, said.

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Gretchen Harrington, 8, was walking to her father’s church for Bible camp on Aug. 15, 1975, when David Zandstra allegedly kidnapped and killed her. (Delaware County District Attorney’s Office)

Zandstra – a husband and father of three – admitted to the crime, District Attorney Jack Stollsteimer announced in July.

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Sullivan interviewed the 83-year-old suspect for her book. At the time, she assumed he had forgotten most details from the decades-old crime. He didn’t seem to have much to offer for the book, unlike his wife, who recalled Gretchen’s disappearance clearly, Sullivan explained.

David Zandstra, 83, of Marietta, Georgia, is charged with criminal homicide; first-, second- and third-degree murder; kidnapping; and possession of an instrument of crime, according to the Delaware County District Attorney’s Office. (Delaware County District Attorney’s Office)

In fact, Zandstra’s one quote in the book is fairly short.

“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 described as “recent” in the October 2022 book. “She said, ‘I thought Gretchen might be with you,’ and I said no. She said, ‘She’s not here.'”

He continued: “Either I called, or I went to Pastor Harrington’s house, and they confirmed that she had left to walk up the street. And I said she’s not here. I must have at that point called the police.”

Joanna Sullivan, who grew up in Marple Township and co-wrote “Marple’s Gretchen Harrington Tragedy” with her childhood friend Mike Mathis, told Fox News Digital that the book “definitely” played a role in Zandstra’s arrest. (Joanna Sullivan)

Gretchen had been walking to the Bible day camp along Lawrence Road in the Philadelphia suburb, where many previous city-dwellers moved to escape urban crime, the morning of Aug. 15, 1975.

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The camp took place at two neighboring churches – Trinity Church Chapel Christian Reformed Church, where Zandstra was a pastor, and the Reformed Presbyterian Church, where Gretchen’s father was a pastor, in Marple. Camp attendees began each day of camp at Trinity.

Gretchen had been walking to the Bible day camp along Lawrence Road in the Philadelphia suburb, where many previous city-dwellers moved to escape urban crime, the morning of Aug. 15, 1975.  (Pennsylvania State Police)

Zandstra was in charge of helping transport campers from Trinity to Reformed in either a blue-and-white Volkswagen bus or in his green Rambler station wagon, the DA’s office said.

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Gretchen’s father was a pastor at Reformed and expressed concern about her whereabouts that morning when she did not show up at the church from Trinity. After news of her apparent disappearance spread through camp that day, Zandstra called the Marple Police Department to report the 8-year-old missing.

Zandstra was a pastor at Trinity at the time and was in charge of helping transport campers from Trinity to Reformed, the DA’s office said. (Google Maps)

The girl’s remains were discovered two months later within Ridley Creek State Park.

One witness reported seeing Zandstra speaking with Gretchen from a green station wagon on Aug. 15. When authorities interviewed Zandstra in October after the victim’s remains were recovered, he denied seeing her that day.

One witness reported seeing Zandstra speaking with Gretchen from a green station wagon on Aug. 15. When authorities interviewed Zandstra in October after the victim’s remains were recovered, he denied seeing her that day. (Pennsylvania State Police)

Earlier this year, the best friend of Zandstra’s daughter, who is named in the criminal complaint filed against the defendant, told authorities that while sleeping over the defendant’s house one evening when she was 10, she awoke to Zandstra groping her.

When the girl “told the defendant’s daughter about what had happened, the defendant’s daughter replied that the defendant did that sometimes,” the DA’s office wrote in a press release.

The informant also recalled that a girl in her class was almost kidnapped twice and showed investigators a journal entry from 1975 expressing her belief that Zandstra was behind the attempted abductions.

Gretchen Harrington had been walking to the Bible day camp along Lawrence Road in the Philadelphia suburb, where many previous city-dwellers moved to escape urban crime, the morning of Aug. 15, 1975. (Joanna Sullivan)

Sullivan said the informant came forward after “Marple’s Gretchen Harrington Tragedy” was published.

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“A woman came forward and offered her diaries and her experience with Zandstra and her feelings that he might have been the one,” the author explained.

Investigators contacted the defendant in Georgia on July 17. Despite initially denying his involvement in the case, Zandstra ultimately confessed to the crime after being confronted with evidence, including statements from his daughter’s best friend.

Sullivan said the informant came forward after “Marple’s Gretchen Harrington Tragedy” was published. (Joanna Sullivan)

The 83-year-old retired pastor admitted to seeing Gretchen walking on the morning of her disappearance, offering her a ride in his green station wagon and taking her to a nearby wooded area. He said he parked the car and asked the girl to remove her clothing. When she refused, he allegedly struck her in the head and believed her to be dead. He then attempted to cover up her body and fled the scene, according to the DA’s office.

Authorities drew up an arrest warrant and complaint on the same day they questioned Zandstra. A Cobb County, Georgia, judge denied bail for the suspect.

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Investigators collected a DNA sample from Zandstra so that it can be compared to evidence in other Pennsylvania cold cases.

Zandstra allegedly kidnapped Gretchen while she was walking to Bible camp in Marple Township in August 1975. (FOX 29 Philadelphia/Delaware DA’s Office)

“There’s no happy ending in this case,” Sullivan said. “But, you know, we’re relieved that justice might occur – that if he’s the killer and convicted, he will pay for the crime.”

Sullivan also noted that she is relieved the case was solved because “people are getting older,” and not everyone was able to witness the case brought to justice, including Gretchen’s father, who died in 2021, and the lead detective on her case, Richard Mankin, who died in 2020. Mankin “made it his life’s mission to try and find this killer,” she said.

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The Harrington family said in a July statement after Zandstra’s arrest that they are “extremely hopeful” the suspect in Gretchen’s murder “will be held accountable.”

“It’s difficult to express the emotions that we are feeling as we take one step closer to justice.… If you met Gretchen, you were instantly her friend. She exuded kindness to all and was sweet and gentle. Even now, when people share their memories of her, the first thing they talk about is how amazing she was and still is… at just 8 years old, she had a lifelong impact on those around her,” they said. “The abduction and murder of Gretchen has forever altered our family and we miss her every single day.”

The family thanked Pennsylvania State Police “for never stopping in their constant search for answers.”