"More from the star witness?" Borgesi cracked, glaring across the room at his onetime friend.
Aponick was the latest in a parade of cohorts turned cooperators to testify against Borgesi in his retrial on racketeering conspiracy charges.
But unlike the other turncoats who were called during Borgesi's first trial, Wednesday offered Aponick his first opportunity to tell his story to a jury.
Prosecutors hope his addition will bolster their claims that Borgesi, 52, continued to run a violent bookmaking and loan-sharking operation from prison with his uncle, reputed mob boss Joe Ligambi.
But defense lawyer Christopher Warren has already described the man as a witness "so damaged, the FBI threw him away."
For his own part, Aponick, 47, told jurors Wednesday that despite enjoying his time with Borgesi, he decided to turn on his cellmate within a month of their moving in together.
Aponick had been moved to the federal detention center in Beckley, W. Va., in 2002 with two years to go on an eight-year sentence for robbery. Borgesi was serving time there on a racketeering conspiracy charge.
And throughout their time together, Aponick fed dozens of Borgesi's purported statements to FBI agents, including boasts of a hit squad he said he ran for the mob, and the 11 murders he claimed to have committed.
"He was telling me all this stuff," Aponick said in a relaxed, nasal rasp - equal parts Brooklyn and Brando. "I already did my time. I didn't want to be a part of it."
Still, the two formed a bond that appeared to go well beyond simple friendship.
They went shopping together with commissary money to buy pottery and handbags made by their fellow inmates, Aponick said.
Borgesi offered to set up his friend in Philadelphia upon his release.
And even after Aponick was let out, the two continued to write each other Christmas and birthday cards.
"We laughed. We joked. We bantered together," Aponick testified. "You're in a little cubicle together day and night. You make the best of it."
By early 2003, though, federal prosecutors thought Aponick might be more useful to them on the outside. They persuaded a U.S. district judge in New York to shave several months off his sentence and then sent him to meet with several Borgesi associates wearing a wire.
Aponick recorded conversations with the likes of Borgesi lieutenant Louis "Bent Finger Lou" Monacello and made several appearances before the grand jury investigating his former cellmate and Ligambi.
But it didn't take long for Aponick to return to his roots as a stickup artist.
Within a year of his release, he was arrested again for robbing a half-dozen banks in New York City, kicked out of the witness protection program for violating the terms of his parole once more in 2012, and deemed so problematic a witness that prosecutors dropped him from their witness list during Borgesi's first trial.
Those later crimes did not come up in testimony Wednesday. But Warren, Borgesi's attorney, mentioned them last month in his opening statements to the jury. He is expected to raise the issue again during his cross-examination this week.
And as testimony wound to a close Wednesday, the lawyer wasn't the only one incredulous to see Aponick on the witness stand.
As federal marshals ushered him back into the courtroom after a break, Ligambi locked eyes with government agents in the front row and shrugged.
"Where do you find these guys?" he said.