Both men were arrested in 2011. Serrano awaits a February trial. Medina pleaded guilty Monday to 16 drug trafficking counts.
But it was during the investigation that brought them down that Cordero showed his true loyalties, prosecutors said Thursday.
Two years ago, agents with the U.S. Drug Enforcement Administration installed a pole camera to monitor activity outside the group's primary hub, a warehouse off of Kensington Avenue. Garcia noticed it and called his brother for information.
Later, when agents conducted a raid on the building, Cordero showed up within minutes to peek through windows and report back to Garcia, prosecutor Maureen McCarthy said. He allegedly told another brother to remove $20,000 in drug proceeds from his home, where he had kept the money for Garcia.
"When the FBI questioned him about his actions, he repeatedly lied," McCarthy said.
McMahon offered a different story. For years, Garcia had worked as an informant and talked often with Cordero about his work, the lawyer said. In fact, Cordero knew Garcia's FBI handler well.
Both brothers, McMahon said, were unaware that agents had dropped Garcia from their roster of trusted moles upon learning he was still actively working a drug corner at Swanson and Somerset Streets.
As for the $20,000 in cash? McMahon maintained his client was holding onto it so his sibling could put a down payment on a piece of property.
At the time of his arrest, Cordero, a 23-year veteran of the force, was assigned to the criminal intelligence unit, tasked with gathering information from the streets and passing that on to other investigators.
If convicted on all counts, he faces up to 35 years in prison.