A federal jury Tuesday convicted a Levittown doctor accused of running a multimillion-dollar pill mill with help from the Pagans Motorcycle Club of drug, money-laundering, bankruptcy-fraud, and other charges.

During 23 days of testimony, the government questioned strippers, former patients, investigators, and Pagans members, all of whom said that William J. O'Brien was a drug dealer who illegally prescribed painkillers.

O'Brien contended that nearly everyone was lying. He called out U.S. Department of Health and Human Services Special Agent Joshua Gill multiple times for not knowing that opioids could be used for headaches.

He also criticized Stephen Thomas, a physician and expert witness called by the government, for the $30,000 he had been paid to review records and testify.

Assistant U.S. Attorney Mary Beth Leahy said prosecutors were pleased with the outcome of the trial in federal court in Philadelphia, with O'Brien, who acted as his own attorney, convicted of 123 of 127 counts.

"We agree with the jury's verdict," she said. "The evidence was overwhelming in this case, and the jury found that out, and found him guilty. . . . At the end of the day, justice prevailed."

After the jury took a half-day to deliberate, it took two hours to read the lengthy verdict.

Marie O'Brien, the defendant's mother, wept at one point as the verdict was being read.

"I don't believe my son is guilty," she said. "I think [the jury] made a mistake, and I don't think they were listening too good."

One of the significant charges against O'Brien was his alleged role in the wrongful death of Joseph Ennis, to whom he prescribed painkillers in December 2013. The jury found him guilty of that charge, which carries a mandatory minimum prison sentence of 20 years.

As the verdict was being read, O'Brien sat calmly, showing almost no emotion.

The trial reached a swift end after the government spent more than 20 days calling strippers, investigators, gang members, and another doctor, all of whom testified that O'Brien was a drug dealer.

O'Brien did not call any witnesses, instead playing a 10-second clip from an FBI interview with one of his patients, Charles Johnson. Johnson called O'Brien a "fat doctor."

"What does my weight have to do with anything?" he said several times during the trial.

Closing arguments were heard Monday. The government summarized its evidence to the court, while O'Brien read a few passages from Judge Nitza Quiñones Alejandro's Bible - including the story of David and Goliath, where he referred to the government as the latter.

Sentencing has been scheduled for Oct. 5.

bohnels@phillynews.com215-854-5912 @Steve_Bohnel