The special grand jury investigating Donald Trump’s efforts to overturn the results of the 2020 presidential election in Georgia has subpoenaed several of the former US president’s legal advisers and political allies.

Court documents show the Fulton county special grand jury has issued subpoenas to members of the Trump campaign legal team, including Rudy Giuliani, and Senator Lindsey Graham, a Republican of South Carolina.

The grand jury is also seeking information from the conservative lawyers John Eastman, Cleta Mitchell, Kenneth Chesebro and Jenna Ellis. Mitchell participated in the phone call between Trump and Brad Raffensperger, the Republican secretary of state in Georgia, that sparked the grand jury investigation.

On 2 January 2021, Trump called Raffensperger and urged him to “find” enough votes to reverse Biden’s victory in Georgia. Raffensperger refused to do so, and the call, which quickly became public, ignited widespread outcry.

The Fulton county district attorney, Fani Willis, launched the criminal investigation weeks after the call was leaked, and Raffensperger testified before the grand jury last month.

The latest round of subpoenas in the investigation indicates the grand jury is seeking additional information about Trump allies’ efforts to meddle with the Georgia results.

In the weeks after the 2020 election, Giuliani repeatedly testified before Georgia legislators about his baseless claims of widespread fraud tainting the state’s results. Graham also reached out to Raffensperger days after the 2020 election and pressed him on whether he could reject all mailed-in votes cast in counties with higher levels of mismatched signatures on ballots. (Graham has denied that allegation.)

The grand jury will continue to gather information about Trump and his allies’ attempts to interfere with Georgia’s election results, and the group will then submit a report about whether the former president or any of his associates should face criminal charges over their efforts. Willis will make the final decision about filing charges in the case.

The newest development comes as the House select committee investigating the January 6 insurrection has looked more closely at Trump’s lies about the 2020 election. Raffensperger testified publicly before the committee last month, and he recounted how his office investigated a number of Trump’s election conspiracy theories and found no evidence to substantiate any of them.

“The numbers are the numbers,” Raffensperger told the committee. “The numbers don’t lie.”