Anthony Magsam, a Philadelphia police officer who has been at the center of a long-running Internal Affairs investigation, resigned from the force earlier this week.
The Daily News reported in August that Magsam, 30, allegedly had stolen automatic weapon parts from the department's Firearms Identification Unit while he was working in the unit in 2009.
Numerous police sources with direct knowledge of the incident said Magsam had confessed when he was confronted by colleagues and returned the parts.
The alleged crime was never reported to higher-ups, however.
Magsam - whose mother, longtime police Sgt. Barbara Feeney, is married to retired Chief Inspector Michael Feeney - was quietly transferred from the FIU to Northeast Philly's 15th District.
The sources said the FIU's commander, Lt. Vincent Testa, helped arrange the transfer and told members of the unit who wanted Magsam held accountable that he had decided how the incident would being handled.
Various sources within the department said earlier this week that disciplinary action is expected to be taken Friday against Testa and another supervisor in the unit who knew about the incident.
When the People's Paper first began inquiring about the case during the summer, Police Commissioner Charles H. Ramsey removed Testa from the FIU and Magsam from the 15th District.
He also replaced the Internal Affairs detective and captain who had been in charge of the investigation, which had lagged for more than a year.
Ramsey asked the U.S. Department of Justice to audit the FIU after more stories surfaced about problems in the unit, including allegations that some weapons had either been lost or shipped out of the unit without being fully examined.
The federal investigators found that eight of the unit's firearms - including a Tec-9 semiautomatic - couldn't be found.
The audit led police officials to implement new security protocols and to restrict the number of people who can have access to weapons that are being examined in the FIU.
In September, the commissioner asked the FBI to determine whether federal charges needed to be filed against Magsam. (Being in possession of stolen or unregistered automatic weapon parts is a violation of the National Firearms Act.)
That same month, SWAT cops searched Magsam's Northeast Philly house and confiscated 51 guns. Several other guns were found at a second location.
It was unclear at the time if any of those firearms were among the ones that had gone missing from the FIU.
Magsam resigned Wednesday, police spokesman Lt. Ray Evers said.
John McNesby, the president of the Fraternal Order of Police Lodge 5, said Magsam did not tell union officials he was planning to leave the force.