Instead of using them in the building, Duncan repackaged the surplus cartridges, then used a city UPS account to ship them to Derek and Danita Willis, an Arkansas couple who ran their own supply store, Assistant U.S. Attorney Tomika Stevens said.
Between 2006 and 2011, the pair paid Duncan $545,000, or less than half what the city paid for them. He even charged the couple shipping costs, Stevens said.
Duncan, 61, of Philadelphia, said little during the hearing other than answering perfunctory questions from the judge. He said he has not worked in about two years, and understood he was not likely to get a job in city government again.
"Did you do all of the things the government said you did?" Du Bois asked him.
"Yes, your honor," he replied.
The scheme came to light in late 2011, when a coworker tipped off the city's Office of Inspector General. The FBI joined the case, and agents placed a camera in the storage room to catch Duncan in the act.
Duncan pleaded guilty to fraud and aiding and abetting. Federal sentencing guidelines recommend a prison term of between 33 and 41 months for the crime. Du Bois scheduled the sentencing for Nov. 20.
Stevens and Duncan's public defender, Elizabeth Toplin, declined to say whether he was cooperating, although the judge agreed to seal the plea agreement and other case documents from public view.
The Willises are scheduled to be tried in October. Robert Gamburg, a lawyer for Derek Willis, said his client maintains his innocence.
"He had no idea that Duncan was doing anything improper," Gamburg said Friday.
Amy Kurland, the inspector general, said employees like Duncan "give honest, hardworking city workers a bad name." She said she hoped more would come forward like the coworker who tipped off investigators to the scheme. That man was honored by the mayor for his cooperation, Kurland said.
"I think that's what changes the culture of the city," she said.
Contact John P. Martin at 215-925-2649, at firstname.lastname@example.org or @JPMartinInky on Twitter.