RALEIGH, N.C. — A political operative working on behalf of a Republican candidate for Congress oversaw an illegal absentee ballot “scheme” and went to elaborate lengths to conceal it, a North Carolina election official said Monday at a hearing that could settle the final undecided House race of last year’s midterms.

The spare and harsh allegation of a “coordinated, unlawful and substantially resourced” strategy opened the North Carolina state Board of Elections hearing with the first public pronouncement of state investigators’ conclusions about a get-out-the-vote effort they came to believe was endemic with fraud and misconduct to benefit Mark Harris, the Republican candidate in the 9th Congressional District.

The state board, comprising three Democrats and two Republicans, has the power to determine whether the election results should be certified or whether a new election should be held in the 9th District, which includes part of Charlotte and a vast stretch of southeastern North Carolina.

Kim Strach, the board’s executive director, and witnesses said that the operation involved forging signatures, completing ballots and mailing them from post offices near the voter’s home, and may have involved more than 1,000 absentee ballots or request forms.

Harris has a 905-vote lead over his Democratic rival, Dan McCready. The seat has been held by Republicans for more than half a century, but state officials last year refused to certify Harris as the winner because of concerns about the voting and “irregularities” in absentee balloting.

Strach said the scheme was masterminded by L. McCrae Dowless Jr., a longtime political operative in Bladen County who worked as a contractor for Harris’ campaign. She did not blame the candidate himself nor say that he had direct knowledge of any misconduct.

Still, board members were told Monday that people working on Harris’ behalf illegally collected absentee ballots and, in some instances, filled in incomplete ballots.

The board will continue hearing evidence on Tuesday.

But the state board’s decision might not be the final word. The House of Representatives has the constitutional authority to be the judge of the elections of its members.

This article originally appeared in The New York Times.