A retired US church pastor who presided nearly half a century ago over the funeral of a kidnapped eight-year-old girl has been charged with her murder.

Gretchen Harrington went missing in the Philadelphia suburb of Marple Township on the morning of 15 August 1975 while attending summer Bible camp.

This year a woman told investigators she believed her best friend's father was the culprit.

David Zandstra, 83, is now charged with murder and kidnapping of a minor.

"He is every parent's worst nightmare," Delaware County District Attorney Jack Stollsteimer told reporters on Monday.

"He killed this poor eight-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 the period after that but for years."

In 1975, Mr Zandstra was pastor at the Trinity Christian Reform Church. Bible camps were held on its premises each morning and he would then transport the children to a second church.

But Gretchen never showed up at the Reformed Presbyterian Church, and it was Mr Zandstra himself who reported her disappearance to police that morning.

Her remains would be found in a nearby wooded area nearly two months later.

The suspect presided over the child's funeral, investigators told CBS News, the BBC's US partner.

Investigators say Mr Zandstra had invited Gretchen into his car once she was out of view of her late father, who had watched her walk up the road from the family home.

A witness interviewed soon afterwards reported seeing the girl speak to the driver of a vehicle similar to Mr Zandstra's green Rambler station wagon.

But when interviewed by police at the time, the pastor denied having seen Gretchen that day.

In January this year, investigators spoke with the best friend of Mr Zandstra's daughter.

She told them she often slept over at their house and, at age 10, once woke to find the pastor groping her.

The woman also showed police a 1975 diary entry in which she wrote: "I think he might be the one who kidnapped Gretchen. I think it was Mr Z."

Mr Zandstra moved several times, living in California and Texas before his arrest last week in Georgia by Pennsylvania State Police, at which point police say he confessed to the crime.

The suspect is being held in a local jail and is due to be extradited to Pennsylvania.

In a statement, the Harrington family said the arrest felt like "one step closer to justice".

"If you met Gretchen, you were instantly her friend. She exuded kindness to all and was sweet and gentle," they wrote.

"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 eight years old, she had a lifelong impact on those around her."