Three weeks before the scheduled start of his trial in Fulton County, a defendant in the Georgia election interference case is seeking to have the indictment against him dismissed based on an alleged paperwork error made by one of the lead special prosecutors in the case.

Kenneth Chesebro, an attorney who drafted legal memos suggesting the use of so-called "alternate electors" to prevent Joe Biden from receiving 270 electoral votes in the 2020 election, is set to go on trial on Oct. 23. But in a filing Wednesday, his attorney alleged that Fulton County special prosecutor Nathan Wade, who was brought in by the district attorney to help investigate the case, didn't file the oath of office required to join the DA's team.

The motion alleges that Wade filled out the oath of office paperwork, but did not file it as required by law until just last week -- an error that Chesebro says makes Wade's work "void as a matter of law."

"Nathan Wade, who has and continues to serve as lead counsel in this case -- including during the presentment of the case to the criminal grand jury and at the time the underlying indictment was returned -- was not an authorized public officer by Georgia law," the filing states.

The filing, from Chesebro attorney Scott Grubman, alleges that Wade did not file either of the required oaths "until September 27, 2023, which was soon after [Grubman] sent Mr. Wade an email inquiring about this apparent lapse (and asking for proof of filing)."

In the filing, Chesebro's attorney urged the judge not to let the alleged paperwork error be "chalked up to mere 'technical noncompliance'"-- warning that it is an error that may rise to a criminal violation.

Former Georgia prosecutor Chris Timmons, however, said that the practice of using special assistant district attorneys is "routine" in the state, and that "at worst" the error would be "embarrassing" for the state -- but not a blow to the entire indictment.

"If he was not sworn in, at worst it's embarrassing for the Fulton County DA's office but it would not affect the case," Timmons told ABC News. "The Georgia Supreme Court has held unanimously that the presence at the grand jury of individuals who are not sworn assistant district attorneys will not vitiate an otherwise valid indictment."

Grubman, however, says in the filing that the Georgia state legislature has made it a misdemeanor crime to "take an actions as a public officer without first taking and filing the appropriate oaths."

"Because Mr. Wade did not file his oaths as expressly required by law, any actions that he took prior to filing the oath on September 27, 2023, are void as a matter of law," the filing states. "This includes presenting this case to the criminal grand jury and obtaining an indictment in return."

"Accordingly, the indictment in this case must be dismissed," the filing says.

Chesebro and 18 others, including former President Donald Trump, pleaded not guilty in August to all charges in a sweeping racketeering indictment for alleged efforts to overturn the results of the 2020 presidential election in the state of Georgia. Defendant Scott Hall subsequently took a plea deal in which he pleaded guilty to tampering with voting machine equipment.

Chesebro's lawyers acknowledge that their client drafted the legal memos at the center of his alleged conduct, but say his actions were justified since Chesebro was "fulfilling his duty to his client as an attorney."

The Fulton County district attorney's office declined to comment to ABC News.

Chesebro's filing comes before another on-camera hearing in the case is scheduled for this week, during which the judge is set to hear a separate motion to dismiss filed by Chesebro's co-defendant, Sidney Powell.