His testimony may be the only word jurors will hear from the accused before defense lawyers are expected to rest their case this week.
Only one former Traffic Court judge, Michael Lowry, signaled Monday that he was still considering testifying.
Several of the others have had run-ins with the law or judicial ethics boards that could cause problems should prosecutors get a chance to question them in front of the jury.
For Judge Robert Mulgrew, that history includes a conviction last year on federal fraud and conspiracy charges. He admitted embezzling thousands of dollars in state funds from a South Philadelphia nonprofit.
Judge Willie Singletary's run-ins with the state Judicial Conduct Board ended in 2012 with a reprimand for showing a photo of his genitals to an employee.
So far, those indiscretions have been kept from jurors hearing the current case, and prosecutors have stuck to their primary narrative.
They allege that Mulgrew, Singletary, and the others participated in a culture of ticket-fixing in Traffic Court and dismissed dozens of citations for friends, family members, and political allies. In doing so, the government says, the judges deprived the city and state of untold revenue in fines and fees.
Bruno maintained Monday that he played no part in what might have been going on in Traffic Court behind chamber doors.
First appointed to the district bench in 1998, Bruno began filling in at the Philadelphia court in 2003 for a few days each year while its regular judges attended training.
Before his first week on the Philadelphia bench was over, he said, he was approached by a Traffic Court cashier seeking a break on behalf of a neighbor.
"Before she said anything else, I laid into her," the judge testified. "I said, 'Ma'am, that's not the way it's done with me.' I think I raised my voice."
And before his testimony concluded Monday, Bruno had the chance to raise his voice again - this time under questioning from prosecutor Anthony Wzorek.
The exchange - at times contentious - centered largely on what Wzorek previously described as Bruno's attempt to fix a speeding ticket for a grade-school friend in 2011.
That man testified in June that after receiving a speeding ticket, he approached Bruno to make sure the offense would not result in points being added to his driving record.
It was only after FBI agents showed up on his doorstep, the man said, that he learned that despite his being found guilty, an appeal had been filed, a lawyer hired, legal documents signed, and a case in Common Pleas Court fought and won - all in his name and without his knowledge.
Bruno testified Monday that he knew nothing about that appeal either. He said he had only asked William Hird, then the court's top administrator, to double-check whether his friend would get points on his record.
Later, when his friend received an unpaid-balance notice for 50 cents, Bruno again sought out Hird, and retired Judge Fortunato Perri Sr., to find out what needed to be done to settle the case.
"It wasn't that important to me," he said. "All I expected was for [Hird] to get back to me on whether there was points."
He did not know that FBI agents were listening in on Perri's calls. And Wzorek hammered him with recordings of those conversations Monday, attempting to show that Bruno was clearly seeking more than an answer to a legal question.
Shouldn't Bruno - as a judge routinely hearing traffic cases himself - know whether a speeding ticket would add points to a driving record without having to call staff at the Philadelphia court, the prosecutor asked. And if his friend's case wasn't that important to him, why did he twice page Hird and then call Perri when he learned his friend had been found guilty?
Wzorek continued his assault later, attempting to goad Bruno into passing judgment on his codefendants. He peppered Bruno with pointed hypotheticals, asking whether it was wrong for judges to discuss their cases with defendants outside of court or promise an outcome before hearing arguments in the case.
"Sounds like an unethical act, sir," Bruno replied.
"Or possibly an illegal act?" Wzorek prompted.
Bruno responded curtly: "That's for the jury to decide."