Numerous police sources previously told the Daily News that Magsam confessed when he was confronted by his colleagues and later returned the parts.
The theft was never reported, and Magsam - the son of longtime police Sgt. Barbara Feeney, who's married to retired Chief Inspector Michael Feeney - was quietly transferred out of the unit.
"They knew what was going on, and it was inappropriate," Ramsey. "There's no excuse for it."
Testa and Little were both cited for neglect of duty and failure to supervise, he said.
Magsam, 30, resigned on Wednesday.
Ramsey said he had intended to fire Magsam, based on the findings of an Internal Affairs investigation that took more than a year to complete.
It's up to the FBI to determine whether Magsam should face criminal charges, he said.
Ramsey asked the feds to investigate the alleged theft in September, a month after the Daily News began reporting on the case.
The commissioner also asked the U.S. Department of Justice to audit the FIU in light of several stories about other problems in the unit.
The audit found that eight firearms - including a Tec-9 semiautomatic - were missing.
SWAT cops later seized 51 guns from Magsam's house, and several others from a separate location.
Ramsey said today that some of the seized firearms were the same models as the ones that were missing from the unit, but their serials numbers had been obliterated - making it impossible to tell if Magsam had stolen them from the FIU.
"We were unable to raise the serial numbers," he said. "That's one we won't know."
Contact staff write David Gambacorta as firstname.lastname@example.org or 215-854-5994.