WASHINGTON—A former Republican Party official helped a computer forensics firm inspect voting equipment in Georgia and then made misleading statements under oath about her role in the episode, voting-rights activists alleged in a new court filing.

The court filing, which includes time-stamped screenshots of surveillance footage, describes what happened inside the Coffee County elections office on Jan. 7, 2021, an episode that is being investigated by law-enforcement agencies in the state.

Screenshots of video footage shows Cathy Latham, a former Republican Party official in Georgia, spending the day at the elections office in the southeast of the state, welcoming representatives of a computer forensics firm called SullivanStrickler, and taking them to a room that stored equipment known as “poll pads,” which contain sensitive voter data.

Mrs. Latham “was a primary facilitator of the breach of Georgia’s voting system,” the court filing alleged, adding that she has made repeated “false statements” about what happened that day.

Mrs. Latham, who now resides in Texas, was one of the dozens of people in seven states who tried to submit false slates of electors as part of an effort to overturn the 2020 election in favor of former President Donald Trump. During the 2020 election, she was chairwoman of the Coffee County Republican Party and oversaw party organizing in many other smaller counties.

An attorney for Mrs. Latham, Bob Cheeley, didn’t respond to an email seeking comment. Mrs. Latham’s lawyers said in a court filing last week that she testified to the best of her memory.

Cathy Latham, bottom, who was the head of the Coffee County Republican Party in Georgia, greets a team from data solutions company SullivanStrickler at the county elections office in this security-camera footage.

Photo: Associated Press

“Failure to have completely accurate recall of the details of events that occurred on a specific date…is not uncommon, and it is a far cry from lying,” the lawyers said.

Atlanta-based SullivanStrickler was hired by Sidney Powell, a former legal adviser to Mr. Trump who helped lead his efforts to challenge President Biden’s victory in the November 2020 presidential election.

“We are on our way to Coffee County Georgia to collect what we can from the Election / Voting machines and systems,” a SullivanStrickler executive said in an email to Ms. Powell on the morning of Jan. 7, 2021, that was disclosed in the litigation.

Ms. Powell didn’t immediately respond to a request for comment. SullivanStrickler didn’t respond to a request for comment. The firm told the Atlanta Journal-Constitution last month that it had “no reason to believe” it was being asked to do anything illegal or improper in visiting the Coffee County elections office.

In a deposition last month, Mrs. Latham testified under oath that she was only very briefly present at the elections office that afternoon and wasn’t involved in SullivanStrickler’s activities that day.

The video screenshots in the court filing contradict that testimony, showing Mrs. Latham arriving at the office at 11:37 a.m., spending much of the day there, and taking a selfie with one of the forensics experts before leaving at 6:19 p.m.

The video footage was obtained by a group of voters and the Coalition for Good Governance, a voting-rights advocacy group. A lawsuit they filed in 2017 has slowly made its way through the court, alleging that Georgia’s touch screen voting machines aren’t secure. 

The lawsuit has taken on newfound significance since the November 2020 election because the plaintiffs have issued subpoenas for Mrs. Latham’s electronic devices. Mrs. Latham’s lawyers have opposed the request, which will be decided by U.S. District Judge Amy Totenberg in Atlanta.

Fulton County District Attorney Fani Willis, a Democrat, has notified Mrs. Latham and the other alternate electors in Georgia that they are targets of her investigation into efforts to overturn Georgia’s 2020 presidential election results.

Write to Jan Wolfe at jan.wolfe@wsj.com