PHILADELPHIA—A jury weighing mob racketeering charges in Philadelphia reviewed FBI wiretaps on Thursday involving the collection of debts from an undercover agent, but it failed to reach a verdict for a third day.

The request to revisit certain tapes suggested the panel was working on charges toward the end of the 52-count indictment.

However, jurors could be deciding individual loansharking and gambling charges before weighing Count One—the racketeering conspiracy charge facing all seven defendants. They include reputed 73-year-old Philadelphia mob boss Joseph "Uncle Joe" Ligambi and 62-year-old underboss Joseph "Moussie" Massimino.

The 13-year FBI investigation is markedly devoid of the murders and shootings that defined the mob a generation ago, a point emphasized by defense lawyers during the three-month trial.

On the secret recordings, defendants can be heard saying the mob today is broke, at least in part due to the growth of legalized, state-sponsored gambling that cuts into their video poker and sports betting operations.

Said one defendant on tape: "It's a broke, broke mob."

Prosecutors believe Ligambi has quietly run La Cosa Nostra in the Philadelphia region since flashy predecessor Joseph "Joey" Merlino went to prison in 1999. Merlino left prison last year and has settled in South Florida. Government officials no doubt sought to keep a lid on organized crime over the past decade, by infiltrating the mob and taping thousands of phone calls, even as the streets of South Philadelphia remained fairly quiet.

There hadn't been a mob hit in the city in nearly a decade when the trial started in October. But that may have changed the day the government rested its case last month and a suspected informant was gunned down in front of his South Philadelphia home. Anthony Nicodemo, a minor gambling figure who lived nearby—and who was linked in the Ligambi trial to a 1998 mob assault—is charged with the daytime slaying of convicted drug dealer Gino DiPietro.

But the motive remains unclear, and the mob trial resumed after the judge questioned jurors about coverage of the killing.

In court Thursday, one juror whose T-shirts frequently salute his love of motorcycles instead turned his sartorial fancy to booze.

"I'm not an alcoholic! They go to meetings," the shirt read.

By comparison, the defendants are often nattily dressed, thanks to suits or sport coats—Massimino's is camel's hair—brought in each day by relatives. Five of the defendants have been in custody for the past 18 months.

Ligambi's wise-cracking nephew, alleged consigliere George Borgesi, has been in prison for 13 years. He was nearing his release from the Merlino case when he was charged in the 2011 indictment. His wife and mother—Ligambi's sister—are among the supporters who trade quips and jokes with the defendants during the breaks.

As the verdict nears, the mood at the defense table has been increasingly festive. Massimino frequently jokes about plans for a celebratory martini when the case ends. He's even joked with the lead prosecutor about needing a ride home.

The jury is set to return Friday for a fourth day of deliberations.