An 83-year-old former pastor has been charged with the kidnapping and murder of a neighboring pastor's daughter in 1975, Pennsylvania officials announced Monday.

The suspect, David Zandstra, was arrested on July 17 in Cobb County, Georgia, where investigators say he confessed to killing 8-year-old Gretchen Harrington nearly five decades ago when he was a pastor in Marple Township, Pennsylvania, according to the Delaware County District Attorney's office in Pennsylvania.

His confession came after investigators presented him with new evidence gathered early this year, which came from an interview with a confidential informant and a diary entry the informant wrote in 1975 when she was a 10-year-old girl, the district attorney's office said in a news release.

Zandstra has been charged with criminal homicide, murder, kidnapping of a minor and the possession of an instrument of crime, the release said.

"Justice has been a long time coming, but we are proud and grateful to finally be able to give the community an answer," Delaware County District Attorney Jack Stollsteimer said in a statement.

This case has "haunted" members of law enforcement and the small area of Marple Township since Gretchen went missing, Stollsteimer said. The girl was last seen walking to summer Bible camp on August 15th, 1975, the release said.

The camp was held at both the Trinity Church Chapel Christian Reform Church -- where Zandstra was a pastor -- and the Reformed Presbyterian Church -- where Gretchen's father was a pastor, the release said. Gretchen's father became concerned when she failed to appear at his church, the release says, and it was Zandstra who then called police to report Gretchen's disappearance.

Investigators noted there were inaccuracies in Zandstra's early statements and they had questions about how the pastor knew so much about what Gretchen was wearing that day, even though she never arrived at camp, according to a newly released criminal complaint.

At the time, Zandstra denied knowing anything about the disappearance, the complaint said.

Two months later, Gretchen's skeletal remains were found in nearby Ridley Creek State Park. Her cause of death was homicide, and the medical examiner said Gretchen suffered "two or more blunt impacts to the skull," according to court documents.

Nearly five decades went by as the case laid dormant. Ultimately, an interview with a woman who was friends with the suspect's daughter in the 1970s -- and her diary entries from that time -- led to a pivotal break in the case.

Decades-old diary entry sheds new light on case

It wasn't until this January that Pennsylvania State Police learned new evidence from the confidential informant, who had been best friends with one of Zandstra's daughters in the 1970s and attended sleepovers at his home, the district attorney's office said.

The woman showed police a diary she kept in 1975 in which she wrote that the then-pastor "touched her groin area" on two occasions while she was attending a sleepover at his home, the complaint said. The informant told investigators when she told Zandstra's daughter what happened, the daughter replied that her father "did that sometimes," the release said.

The informant's diary also contained an entry about a separate incident, which she said was an attempted kidnapping.

"Guess what? A man tried to kidnap Holly twice! It's a secret so I can't tell anyone, but I think he might be the one who kidnapped Gretchen," read the diary entry from September 1975, according to the criminal complaint. "I think it was Mr. Z."

Investigators learned the former pastor now lives in Marietta, Georgia, and confronted him there with the new evidence last month, according to the release.

Zandstra admitted he offered Gretchen a ride to the summer camp the morning of her disappearance, according to the complaint. He told officers he drove the child to a wooded area and told her to take off her clothes, the complaint said. When she refused, he said he punched her in the head and left her bleeding in the area, believing her to be dead, according to the complaint.

A DNA sample was collected from Zandstra by police so it can be compared to DNA collected from the scene, as well as open cases in the state and country, the district attorney's office said.

"The abduction and murder of Gretchen has forever altered our family and we miss her every single day," the Harrington family said in a statement provided by law enforcement.

"We are grateful for the continual pursuit of justice by law enforcement and we want to thank the Pennsylvania State Police for never stopping in their constant search for answers."

Zandstra left Pennsylvania after Gretchen's disappearance and lived in Plano, Texas, and Marietta, Georgia, prosecutors said.

Pennsylvania State Police are now asking people in those communities who may have relevant information about Zandstra to contact them.

CNN reached out to Zandstra's listed attorney on court documents but did not hear back.