The known claims are concentrated in Bladen County, which has about 33,000 residents, and neighboring, far larger Robeson County. Bladen County, where elections officials work in a simple brick-and-glass building on South Cypress Street, just behind a shopping center with a Dollar General and a furniture store, recorded the state’s highest rate of absentee ballot requests: 7.5 percent of registered voters, compared with less than 3 percent in most of the other 99 counties.

A strikingly large number of those ballots, 40 percent, were never returned. In Robeson County, 62 percent were not returned. No other county had a rate higher than 27 percent. Mr. Harris won 61 percent of submitted absentee ballots in Bladen County, even though registered Republicans accounted for only 19 percent of the ballots submitted.

Those statistics, coupled with the alleged and acknowledged machinations of Mr. Dowless, who has a felony record and a history of financial fraud, and his workers sparked what slowly swelled into another bitter electoral impasse in a state that seems perpetually engulfed by them.

On Tuesday, the district attorney for the area, Jon David, said law enforcement officials were investigating allegations related to the 2016 elections and were in contact with each other “to coordinate our efforts should a prosecution be warranted” in the wake of this year’s suspicions.

Almost all the worries, for now, involve absentee ballots. In an affidavit, a Bladen County resident, Emma Shipman, wrote that she had recently handed over her ballot to a woman who told her that she was assigned to collect ballots in the district. Another voter wrote that she gave her incomplete ballot to a woman who promised she would finish it.

State officials are also reviewing other claims. Mr. Malcolm, the elections board chairman, said Tuesday that the authorities would release documents on “a rolling basis in a manner reasonably calculated to serve the public interest without compromising the investigation.”

Perhaps no figure is more central to that inquiry — or the subject of more rumors and speculation — than Mr. Dowless, who was assigned to get-out-the-vote efforts in the eastern part of the Ninth District, which runs from Charlotte to east of Fayetteville.