According to Commissioner Danielle Outlaw, the child has been identified as Joseph Augustus Zarelli.
Joseph was born on January 13, 1953, and is believed to be from West Philadelphia.
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The child's naked, badly bruised body was found on Feb. 25, 1957, in a wooded area of Philadelphia's Fox Chase neighborhood. The boy, who was 4 years old, had been wrapped in a blanket and placed inside a large JCPenney bassinet box. Police say he was malnourished. He'd been beaten to death.
"This announcement only closes one chapter in this little boy's story while opening up a new one. This is still an active homicide investigation and we still need the public's help in filling in this child's life story," Outlaw said.
His remains had never been identified until now. The case is one of Philadelphia's oldest unsolved homicides.
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"Without the hard work, dedication, passion and doggedness of the many we would not be here today to give America's formerly unknown child Joseph Augustus Zarelli a voice," Outlaw said.
Commissioner Outlaw reveals the name of the 'Boy in the Box'
"It was determined the case of the unknown child...would benefit from the application of modern forensic techniques," Philadelphia Captain Jason Smith said.
Police said both of Joseph's parents are dead, but he has living relatives.
Philadelphia police Captain Jason Smith reveal details on 'Boy in the Box' case
"Joseph has a number of siblings on both the mother and father side who are living and it's out of respect for them that their parents' information remain confidential," Smith said.
Smith also said Thursday police do not know who is responsible for the child's death.
"We have our suspicions as to who may be responsible but it would be irresponsible of me to share these suspicions as this remains an ongoing and active criminal investigation," he said.
SEE ALSO: Genealogist who helped identify 'Boy in the Box' visits grave, seeks justice for child
The boy's missing identity gnawed at police officials, generations of whom took up the case.
Bill Kelly took the young victim's fingerprints at the scene back in 1957. His family says he never stopped trying to find out the boy's identity or assailant up until his death.
"He was one of the first on scene that fateful day. 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," said Kelly's granddaughter, Jessica Greene, who knew him as Pop-Pop.
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"I was thinking my father would be so happy ... so happy," said Kathleen Kelly Greene, who is Jessica's mother.
When news spread last week that Philadelphia police would hold a news conference revealing the boy's identity, it sent shock waves through the community. It hit home to the children of the people who worked the case and had hoped to see a resolution in their lifetime.
Kym Durham is a psychic medium in South Jersey. She has assisted law enforcement in missing persons and homicide cases. Her gift, as she describes it, was passed down from her mother, internationally renowned psychic medium Joan Friel Durham.
Joan Durham even received an award from the Vidocq Society, the prestigious group of law enforcement tasked with solving cold cases, including the "boy in the box." Joan has since passed but her daughter remembers her mother receiving a call in the 80s to assist with the now 65-year-old cold case.
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"She talked about this person - a male - she talked about the nose," said Kym about a man her mother described as someone being involved.
Independent of each other, both Bill Kelly and Joan Durham gave a name to the victim. Kelly called him Jonathan; Durham called him Johnny.
Both families say they are glad to see an update on the case.
"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," said Jessica Greene.
The case still remains unsolved. There is a $20,000 reward for information that leads to an arrest and conviction of a suspect in this case.
The Associated Press contributed to this report.