For nearly 20 years, retired minister David Zandstra lived in a quiet neighborhood north of Marietta, where neighbors knew him as a grandfatherly figure who walked their cul-de-sac with the help of a cane and exchanged pleasantries with those he passed.

Residents of the Lakewood Colony subdivision were taken by surprise when they learned Zandstra had been arrested last week. The 83-year-old, once thought of as an “exemplary neighbor,” now stands accused of killing an 8-year-old girl nearly 50 years ago in Delaware County, Pennsylvania — a case that for decades had gone cold.

Zandstra and his wife moved to Cobb County in 2005 after 40 years of ministry in several congregations within the Christian Reformed Church. It was while serving one of those churches that investigators say he abducted and murdered Gretchen Harrington, a camper at a summer Bible school, in 1975.

The former minister allegedly confessed to the crimes at Cobb police headquarters July 17 and has remained jailed ever since.

Amid his neighborhood’s manicured lawns and well-kept homes, Zandstra’s house stood still Tuesday. No one answered the door. Matthew Poleon, who lives a few doors down, said he was sad to hear the news.

“Every time I was out doing yard work, he would give me a little wave or something,” he said. “I guess he liked seeing people out there working on their yards.”

Another neighbor, who declined to give his name, said of Zandstra: “For fifteen years, he was an exemplary neighbor. That’s all I can tell you. Other than that, I would rather not say anything.”

A 1975 photo of the Trinity Church Chapel, where 8-year-old Gretchen Harrington was attending summer Bible school.

Delaware County District Attorney’s Office

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Delaware County District Attorney’s Office

On the morning of August 15, 1975, Gretchen was last seen walking to camp at Trinity Church Chapel, where Zandstra was the pastor. When she didn’t arrive, her father — a reverend at a neighboring Presbyterian church also participating in the Bible school — reported her missing that same morning. Her body was found two months later about six miles away at Ridley Creek State Park.

There were several leads early in the police investigation, officials said, and some even pointed to Zandstra’s involvement. In one of his initial interviews, Zandstra gave a suspiciously specific description of the shorts Gretchen was wearing the day she disappeared, detectives noted in the criminal complaint. But he maintained he never saw Gretchen, because she never made it to church.

A 1975 newspaper clipping of The Bulletin newspaper about the disappearance of 8-year-old Gretchen Harrington.

Delaware County District Attorney’s Office

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Delaware County District Attorney’s Office

No evidence materialized to lead to an arrest. Still, Gretchen’s case remained open.

“This case has been investigated by generations of detectives, and they all are owed a debt of gratitude for never giving up,” Lt. Jonathan Sunderlin of the Pennsylvania State Police said in a statement.

It was not until January of this year that new evidence came to light: the diary entry of a 10-year-old girl.

The girl, now a woman identified by police only as an informant, recalled a disturbing sleepover at Zandstra’s house. She said she was best friends with one of Zandstra’s daughters and detailed an incident in which he allegedly groped her, according to the criminal complaint. When she told her friend about it, the friend said, “He does that sometimes,” detectives noted.

A 1975 photo of the scene where the body of 8-year-old Gretchen Harrington was found.

Delaware County District Attorney’s Office

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Delaware County District Attorney’s Office

About a week after the sleepover, Gretchen was abducted. The following month, the informant wrote an entry in her diary, intimating that one of her friends was nearly kidnapped.

“Guess what?” the Sept. 15, 1975, entry read. “A man tried to kidnap (friend) twice! It’s a secret I can’t tell anyone, but I think he might be the one who kidnapped Gretchen. I think it was Mr. Z.”

That was enough for detectives to interview Zandstra again, and he agreed to meet them at the Cobb police station. After initially denying his involvement, prosecutors said Zandstra was confronted with the informant’s testimony and admitted to seeing Gretchen walking alone that August morning.

What followed, according to Delaware County District Attorney Jack Stollsteimer, was the first account of what may have happened to Gretchen.

A 1975 photo of Lawrence Road, where 8-year-old Gretchen Harrington had been walking when she was abducted.

Delaware County District Attorney’s Office

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Delaware County District Attorney’s Office

According to investigators, Zandstra said he offered the girl a ride to the Bible school, and since she knew him well, she got into his green Rambler station wagon. But instead of taking her to church, he took her to a nearby wooded area and said he asked her to remove her clothes. When she refused, he told investigators he hit her in the head with his fist. Believing she was dead, he said he attempted to cover her partially nude body and left.

In a statement, the girl’s family said it’s difficult for them 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,” the Harrington family said. “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.”

The Zandstras moved to Plano, Texas, shortly after Gretchen’s death. He served at two other churches in California before retiring, according to the denomination’s website. It was not clear if he was serving in any capacity at a church in metro Atlanta before his arrest.

Officials with the GBI and Cobb County said Tuesday they have no open cases involving Zandstra. According to Stollsteimer, the 83-year-old is fighting extradition, and officials are seeking a warrant through the governor’s office.

“We’re going to try him. We’re going to convict him. And he’s going to die in jail,” the district attorney said during a news conference Monday announcing the arrest. “And then he’s going to have to find out what the God he professes to believe in holds for those who are this evil to our children.”

A DNA sample has been collected from Zandstra and will be compared to open cases across the country.

One such case involves the 1991 disappearance of 4-year-old Amanda Campbell in Fairfield, California, where Zandstra ended his career in ministry. Law enforcement there confirmed they have reopened the case in light of his arrest.

Zandstra lived within 3 miles of Campbell’s home at the time she went missing, records show, and she has never been recovered. His church, the Fairfield Christian Reformed Church, was just over 3 miles away.

“A detective from the Special Victims Unit has been assigned to the case for follow up,” said Jennifer Brantley, a spokesperson for the Fairfield Police Department. “Further details will be provided after detectives had had an opportunity to investigate and speak with the involved allied agencies in Pennsylvania and Georgia.”

Cobb police would not confirm if they had been contacted by the California agency.

— Staff writer Jeremy Redmon contributed to this article.