(CNN) As North Carolina officials investigate allegations that absentee ballots were tampered with in a tight congressional race, a review of some of those ballots revealed many were signed by the same small group of people -- some of whom are connected to a longtime operative working for the Republican candidate's campaign.

North Carolina requires witnesses to sign absentee ballots. Usually, those witnesses are family members or friends.

But a set of 161 absentee ballots for the 9th Congressional District obtained by CNN on Monday showed that the same nine people signed at least 10 absentee ballots each.

Many of those nine people who signed ballots seem to know each other, checks of public records and their social media accounts showed. Some are also associates of Leslie McCrae Dowless, a longtime North Carolina operative who worked for the campaign of Mark Harris, the Republican who leads the race by 905 votes.

A CNN review found three witnesses signed more than 40 ballots each, another signed 30, and three other people signed more than 10 apiece. North Carolina election law states only the voter or a near relative can hand in an absentee ballot.

Their signatures on multiple ballots and connections to Dowless were first published by Judd Legum, the author of the progressive newsletter Popular Information.

Jeffrey Smith, a former friend of Dowless' who used to rent office space to him, said Dowless has teams of people working with him.

"He gets workers to go get people to sign up on a sheet of paper for an absentee ballot," Smith said in a phone interview with CNN. "Say you live in a Section 8 housing area, they will collect these requests. He says you don't have to leave your house, you can just vote at home."

Smith added Dowless then sends people to "harvest" the ballots and he mails them to the election office.

Dowless, 62, has denied any wrongdoing to The Charlotte Observer. He could not be reached on Monday by phone or on Sunday at an address listed for him in voting records.

Dowless pleaded guilty to insurance fraud in the early 1990s after taking out a $163,000 policy on a dead man, court records show.

The absentee ballot signatures are being scrutinized as North Carolina elections officials are investigating allegations of improper activities -- which could ultimately lead to a new election.

Harris, a Baptist minister, led Democratic former Marine and businessman Dan McCready by 905 votes after all the ballots were counted.

But last week the bipartisan State Board of Elections and Ethics Enforcement delayed certifying Harris as the winner after receiving affidavits from voters alleging that people had come to their doors offering to help fill out and return absentee ballots. Democrats submitted an affidavit from someone who alleged they overheard that Dowless would be paid a $40,000 bonus if Harris won the race.

Rather than certifying the election, the board launched an investigation and called for another hearing on or before December 21.

The allegations are focused on Bladen County, where results for votes cast via absentee ballots were much more favorable for Harris than other votes were in both the primary and general election. In ousting Republican Rep. Robert Pittenger in the primary, he won 437 absentee votes in Bladen County to Pittenger's 17, though there was no allegation of ballot tampering in that race.

This year, Harris won 420 absentee votes in the general election in Bladen County to McCready's 258.

On Twitter last week, Harris said he supports the investigation. There is no indication he's been involved in any malfeasance.

"Make no mistake, I support any efforts to investigate allegations of irregularities and/or voter fraud, as long as it is fair and focuses on all political parties," he said in a tweet. "There is absolutely no public evidence that there are enough ballots in question to affect the outcome of this race."

Michael Bitzer, a politics professor at Catawba College, also pointed out an unusually high percentage of absentee ballots that were requested but not returned in Bladen and Robeson counties.

In Bladen, about 40% of the requested absentee ballots, or 495 ballots, were not returned. In Robeson, about 62%, or 1,180 ballots, were not returned. Both percentages are much higher than the district's non-return rate, which was 24%.

"In addition, if ballots were manipulated without the registered voter's knowledge, and votes were changed or spoiled to negate a vote, that would raise serious concerns about the integrity of the 9th Congressional District's election," Bitzer wrote

The North Carolina Republican Party on Friday called for the chairman of the elections board, Democrat Andy Penry, to be removed. Over the weekend, Penry resigned.

"The investigation should be free of attempts at distraction and obstruction so that the truth can be revealed. I will not allow myself to be used as an instrument of distraction in this investigation," Penry said in a statement.

On Monday, North Carolina Democratic Party Chairman Wayne Goodwin said the GOP should not "stand in the way of uncovering the truth."

"These allegations are incredibly serious, and if true, they outline a calculated effort to illegally undermine our free elections and to sway the election in favor of a specific candidate," he said.