Dozens of Philadelphia police officers gathered Thursday in North Philadelphia to mark the 50th anniversary of the murder of Officer Frederick Cione, the only unsolved killing of a police officer in city history

Cione, 25, a first-year officer, was working alone on an overnight shift Jan. 30, 1970, when he was fatally shot in the chest on the 1700 block of West Oxford Street around 1 a.m.

Homicide Lt. Norman Davenport said Thursday that many details surrounding Cione’s killing “remain a mystery to this day,” and he encouraged witnesses to come forward.

Over the years, dozens of people have been questioned, at least two men claimed responsibility, and billboards promised reward money. But nothing materialized as a solid lead.

Davenport acknowledged that it might be difficult to build a criminal case after so many years, but he said: “Every family is deserving of the truth.”

Cione’s relatives — including two nephews who are on the force — attended the ceremony at the site of the killing. Acting Commissioner Christine M. Coulter and Managing Director Brian Abernathy also spoke.

Cione’s brother Nicholas Cione Sr. said officers have frequently told him where they were the night Frederick Cione was killed.

Coulter said: “We want to solve every murder,” and she encouraged witnesses in Cione’s case or any others to come forward.

“Make a difference if you see something,” she said. “Make a difference if you know something.”