One of the 19 defendants in a Georgia racketeering case against former President Donald J. Trump and his allies pleaded guilty on Friday to five misdemeanor charges, under a deal with prosecutors in which he would receive five years of probation.
The guilty plea of Scott Hall, 59, a Georgia bail bondsman, was a significant victory for Fulton County District Attorney Fani T. Willis, who secured an agreement from Mr. Hall to testify against other defendants. No other defendants have taken pleas; two of them, the lawyers Kenneth Chesebro and Sidney Powell, are scheduled to be tried together starting next month after demanding speedy trials.
Mr. Hall had been charged with racketeering, as well as six other felonies, for helping to carry out a breach of voting equipment and data at the elections office in rural Coffee County, Ga., in January 2021 after local pro-Trump officials let them in. He and other Trump allies were apparently looking for evidence of ballot fraud after Mr. Trump lost the 2020 presidential election in Georgia.
More broadly, the indictment handed up in August accuses Mr. Trump and the other defendants of a criminal conspiracy in which they tried in a number of ways to overturn the election results in the state.
Appearing in a Fulton County courtroom before Judge Scott McAfee on Friday afternoon, Mr. Hall, wearing a dark suit and open-necked shirt, pleaded guilty to five misdemeanor counts of intentional interference with performance of election duties.
Under the terms of the deal, Mr. Hall is to pay a $5,000 fine, surrender his firearms carry license, perform 200 hours of community service and write a letter of apology to the people of Georgia. He is not to participate in any activities related to the administration of elections, and he agreed to testify truthfully against other co-defendants if called upon to do so.
The development may have dealt a particular blow to Ms. Powell, just weeks before her trial date. She and Mr. Hall took part in a plan by Trump allies to access election equipment in Coffee County, about 200 miles from Atlanta, in January 2021, according to the indictment.
In a separate hearing on Friday morning, Judge McAfee announced that 450 potential jurors would be called to the courthouse on Oct. 20 to fill out a questionnaire ahead of the trial of Ms. Powell and Mr. Chesebro, who is accused of devising a plan to recruit a group of bogus pro-Trump electors.
That trial, which would be the first related to the four criminal cases in which Mr. Trump has been charged this year, will be closely watched by lawyers for the former president and the other remaining defendants, whose trials have not yet been scheduled.
Melissa D. Redmon, an assistant law professor at the University of Georgia and a former Fulton County prosecutor, said that Mr. Hall’s plea deal on Friday shows “that the state is working to shore up their evidence” in advance of Mr. Chesebro’s and Ms. Powell’s trial. She said the deal was “a good result for the state in that they have someone inside that conspiracy.”
Mr. Hall’s cooperation could potentially cause problems for some of her co-defendants, including two others accused of involvement in the data breach: Misty Hampton, a former Coffee County elections supervisor, and Cathy Latham, a former head of the county’s Republican Party.
Mr. Hall could also provide information about other defendants accused of taking part in an effort to elicit a false confession from a Fulton County elections worker, Ruby Freeman, in the days before Congress certified the national election results on Jan. 6, 2021. The indictment states that Mr. Hall was involved in a phone call with a co-defendant, Trevian Kutti, a day after Ms. Kutti met with Ms. Freeman in an Atlanta suburb.
The impact of Mr. Hall’s cooperation on Mr. Trump was less clear. But securing testimony from any defendant in a racketeering case can strengthen prosecutors’ ability to convince jurors of the existence of the “criminal organization” they lay out in their indictment.
Mr. Hall is the brother-in-law of David Bossie, a prominent early Trump supporter and longtime conservative operative. The August indictment of Mr. Trump and his allies mentions an email in which David Shafer, the head of the Georgia Republican Party at the time of the 2020 election, wrote that Mr. Hall “has been looking into the election on behalf of the President at the request of David Bossie.”
Mr. Shafer is also a defendant in the case.
A team of Trump allies visited Coffee County, about 200 miles southeast of Atlanta, on Jan. 7, 2021. “We scanned every freaking ballot,” Mr. Hall recalled in a recorded phone conversation at the time, adding that his team had “scanned all the equipment” and “imaged all the hard drives” that had been used on Election Day.
Brad Raffensperger, Georgia’s Republican secretary of state, subsequently replaced the voting machines and has referred to what took place as “the unauthorized access to the equipment that former Coffee County election officials allowed in violation of Georgia law.”
Ms. Powell became well known for her appearances after the 2020 election with Rudolph W. Giuliani, another defendant in the Georgia case who was then Mr. Trump’s personal lawyer. Both lawyers advanced numerous conspiracy theories about the election.
But the case against Ms. Powell in Georgia is centered on her actions related to Coffee County. A recent legal filing by Ms. Powell claims that she did not “plan or organize” the data breach that took place, but emails between Ms. Powell and SullivanStrickler, a company hired to help carry out the work that day, shows that she was kept informed of what was taking place and that her nonprofit, Defending the Republic, paid the company.
Other co-defendants in the case suffered significant setbacks on Friday. U.S. District Court Judge Steve C. Jones on Friday denied efforts by Mr. Shafer, State Senator Shawn Still and Jeffrey Clark, a former high-ranking Justice Department official, to have their cases moved to federal court, where the jury pool would be somewhat more favorable to Mr. Trump.
Judge Jones had already rejected a removal effort by Mark Meadows, Mr. Trump’s former White House chief of staff who is also a defendant in the case. Mr. Meadows has appealed that decision.