RALEIGH, N.C. (Reuters) - A Republican operative directed an unlawful absentee ballot scheme in North Carolina’s 9th congressional district and tried to hide the evidence, an election official said on Monday at a hearing that could lead to a new vote in the disputed contest.

FILE PHOTO: Mark Harris, Republican candidate from North Carolina's 9th Congressional district speaks as U.S. President Donald Trump looks on during a campaign rally in Charlotte, North Carolina U.S., October 26, 2018. REUTERS/Kevin Lamarque/File Photo

Republican candidate Mark Harris leads Democratic rival Dan McCready by 905 votes out of 282,717 ballots cast in the November 2018 congressional election.

But the U.S. House of Representatives seat has remained vacant, with state officials refusing to certify Harris as the winner due to accusations of election fraud in two counties in the district.

Kim Strach, executive director of the state election board, on Monday said investigators had uncovered a “coordinated, unlawful and substantially resourced absentee ballot scheme” orchestrated by a political operative working for Harris.

Strach said operative Leslie McCrae Dowless hired workers to collect absentee ballot requests from voters and then return to retrieve the ballots, in violation of state law.

In some instances, the paid workers falsely signed as witnesses and filled in votes for races left blank at Dowless’s home or office, Strach said.

Dowless attended the hearing in Raleigh but declined to testify voluntarily after the board said it would deny him immunity.

Dowless’s lawyer, Cynthia Adams Singletary, said afterward that “he hasn’t done anything wrong.” Harris has said he was unaware of any wrongdoing.

Lisa Britt, who worked for Dowless on the absentee ballots, testified that he instructed his workers to fill in responses for races left blank to avoid “red flags” with the local elections board. She said she was not told how to vote in those races.

“What I would do is vote for whoever was the Republican,” she said.

Britt also said Dowless tried to prevent her from testifying at Monday’s hearing by asking her to invoke her Fifth Amendment right against self-incrimination.

Investigators found Dowless sought to avoid detection by instructing those who worked for him to deliver ballots in small batches to a post office close to the voters and to ensure the same color ink was used for the voter and false witness signatures, Strach said.

Dowless and his workers handled at least 788 ballot requests in Bladen County and 231 in Robeson County, the two counties at the center of the state probe, Strach said.

Voter Kimberly Sue Robinson testified that she returned a blank, unsealed ballot to Dowless representatives.

“I was told if I didn’t fill it out, it would get filled out for me,” Robinson said.

Under state law, the five-member elections board can call a new election if the number of contested votes would sway the original election or if the “irregularities or improprieties occurred to such an extent that they taint the results of the entire election and cast doubt on its fairness.”

Alternatively, the board could certify Harris as the district’s congressional representative.

Republicans have pushed for that outcome, while Democrats want a new election. The hearing resumes on Tuesday.

If the Democrats pick up the seat, they would widen their 235-197 majority in the House after taking control of the chamber from President Donald Trump’s fellow Republicans in the Nov. 6 election.