The first guilty plea in the sprawling Georgia election interference case could put prosecutors right inside Donald Trump's inner circle.

Scott Hall, a 59-year-old bail bondsman who prosecutors say played a key role in the former president's effort to overturn his election loss, pleaded guilty Friday to five misdemeanor counts of conspiracy to commit intentional interference with the performance of election duties and agreed to testify in a case involving 18 other defendants.

Hall agreed to serve five years of probation as part of the deal, and his testimony could prove to be key in the prosecutions of pro-Trump lawyer Sidney Powell, whose trial is set to begin Oct. 23, and former Justice Department official Jeffrey Clark.

His testimony could also provide insight into actions taken by Trump himself to overturn his 2020 loss in Georgia.

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Hall is the brother in law of Republican operative David Bossie, a former deputy Trump campaign manager in 2016 and chairman of the conservative activist group Citizens United.

According to a Nov. 20, 2020, email written by then-GOP chairman David Shafer, who has also been indicted, Hall was acting at Bossie's request, and he would likely be able to tell prosecutors what role the former president and others in his orbit encouraged or directed his actions.

"Hall ... believed that something nefarious had gone on in Georgia during the election," reported Anna Bower for Lawfare. "On Nov. 17, as Trump’s legal team prepared litigation in Georgia, Hall and his wife, Robin, reached out to Wood, claiming that they had 'proof' of voter fraud in Fulton County. 'We watched them count boxes of mail-in votes that were 100% Biden and 0% Trump,' Robin wrote in an email to [attorney Lin] Wood."

Hall later gave sworn testimony in an affidavit filed by Wood in a lawsuit against Georgia secretary of state Brad Raffensperger seeking to halt certification of the state's election results, and he swore that he had observed hundreds of ballots that appeared to be pre-printed with Joe Biden's name.

He then testified Dec. 3, 2020, subcommittee hearing of the state Senate Judiciary Committee with Phil Waldron, John Eastman, and Russell Ramsland, and by early January was in direct contact with Justice Department official Jeffrey Clark -- who was indicted in Georgia and named as an unindicted co-conspirator in Trump's Jan. 6 federal indictment.

Clark cited Hall's claims in a Jan. 2, 2021, conversation with two other Justice Department officials he urged to send a letter to state officials in Georgia and other swing states asking them to hold special legislative sessions to hear evidence on election fraud, and recommended they send an "alternate" slate of pro-Trump electors.

The indictment shows that Clark and Hall spoke by telephone for 63 minutes on that day.

Hall then flew down to Coffee County from Atlanta and was present when local GOP chair Cathy Latham, local elections officials Misty Hampton and Eric Chaney, and former elections board member Ed Voyles went inside the elections office with employees from the forensics firm SullivanStrickler.

Latham spent more than four hours inside the office as SullivanStrickler employees created copies of nearly every piece of the county's election equipment, and court filings show they were acting on orders from Powell, who was then part of Trump's legal team.

Latham, Hampton and Powell have each been indicted as part of the racketeering case.