Police reveal identity of the 'Boy in the Box' after murder mystery of nearly 66 years

Police have revealed the identity of the infamous "Boy in the Box" as Joseph Augustus Zarelli.

Also known as "America's Unknown Child," Zarelli was found in the Fox Chase neighbourhood of Philadelphia, Pennsylvania in 1957.

Little Joseph was found wrapped in a blanket inside a large JCPenney bassinet box. He was naked and had been beaten and showed signs of malnutrition.

Thanking the detectives who worked on the case Police Commissioner Danielle Outlaw said: "Today, after 65 years, America's Unknown Child's name was finally restored. I want to thank all who have worked tirelessly since 1957 to give Joseph Augustus Zarelli his voice back.

"However, the search for justice continues."

At the time, his face was put on a poster as police tried to catch the killer, but nobody was identified and the child was buried in a grave that read "heavenly father bless this unknown boy."

Police said they have a suspect, but that it would be "irresponsible" to name them at this time.

Zarelli, born on January 13, 1953, was finally identified after a painstaking process by genealogists helped to identify his father. Police said they would not name the parents of the child out of respect for Joseph's siblings.

The naming of the victim of Philadelphia's longest unsolved homicide case will come as some relief to police officers who worked on the investigation, as well as the families.

Before the press conference, police confirmed they would be able to reveal the boy's identity, leading the families of some detectives to express their relief.

Bill Kelly took the fingerprints of the boy on the day he was found. His granddaughter Jessica Greene said "Pop-Pop" never forgot the image of what he found.

"He was one of the first on scene that fateful day," she said to ABC. "He never forgot about that image. I mean how could you? ... He was the fingerprint expert on scene.

"Those fingerprints were ingrained in his mind his whole life, and when he closed his eyes in his mind that's what he saw."

Jessica's mum Kathleen added: "I was thinking my father would be so happy... so happy."

Experts from the Vidocq Society took up the case and detectives also exhumed the body for analysis before taking it back to a grave site in 1998.

Jessica added: "I think as a family that's why it's important, not just us, but America's unknown boy has this identity revealed.

"But now with his ID coming to the forefront, we can piece together some of the theories they had in the past."

The family of Detective Tom Augustine, who was a pallbearer when the body was reburied, said the news of the identity brought them "closure."

"We grew up with those posters plastered in his office, in his house," grandson Matthew Braxton said to Action News.

"We grew up knowing at a very young age who this was. It was a big part of not only his life, but our life. So it's kind of closure for us too."

Outlaw said Augustine and colleagues showed "unending dedication" to the case.

Zarelli's grave will now be updated to mark the landmark discovery.