A ballot-fraud investigation that has already troubled two top Miami-Dade political campaigns has now embroiled the office of a county commissioner and could result in the arrest of the uncle of Hialeah’s former mayor, The Miami Herald has learned.

As part of the widening probe, police identified 164 absentee ballots collected at Commissioner Esteban Bovo’s Hialeah office, where an aide delivered them to a local post office, according to sources close to the investigation.

Bovo said he was shocked and knew nothing of the investigation, which has vexed the reelection campaigns of the county mayor and prosecutor.

Bovo’s aide is cooperating with law-enforcement authorities and, sources said, identified Sergio “ Tío” Robaina as one of the three brokers — known as boleteros in Spanish — who dropped off the ballots at the commissioner’s Hialeah district office, which was used as a central-collection point last month.

Robaina denied dropping off ballots at Bovo’s district office. He’s the uncle of former Hialeah Mayor Julio Robaina, who couldn’t be reached.

“I never left anything there. I didn’t leave a single ballot,” Robaina, 74, said. But he admitted that “sometimes” he does collect ballots and mails them. “I have always collected ballots of different people, even for Esteban Bovo.

“People call and ask for ballots. Then, you go and they put a seal on it and they send it,” Robaina said. “I’ve collected ballots because the person can’t. But mostly they send them. They have to be very old or something. And the ballots have to be sealed.”

Voter Barbara Pino, 52, who is deaf and mute and uses crutches to walk, cast one of the 164 ballots being examined by police. When asked by an El Nuevo Herald reporter who collected her ballot, she wrote on a notepad: “Sergio Robaina.”

Voter Maria Pena, 52, also said Robaina came by recently to recommend candidates, though she did not remember which. She said she dropped her own ballot in a mailbox near a J.C. Penney.

Deisy Cabrera, 56, is the only ballot broker charged so far. She was arrested on charges of forging a voter’s signature on a ballot and violating a county ordinance that prohibits third parties from possessing more than two absentee ballots of other voters.

Commissioner Bovo has not been questioned by police. Thursday night he said he was surprised by it all.

“Jesus, how am I supposed to comment on something like this?” Bovo said. “This is the first I’ve heard of any of this. Working for any other campaign on county time and in my office is prohibited. It shouldn’t have happened.”

Bovo’s aide, Anamary Pedrosa, no longer works at his office.

She submitted her resignation July 23 and stopped working at the Hialeah office July 27, two days after investigators believe she delivered to the post office the 164 ballots that had been dropped off. Bovo said his aide quit because she wanted to go to law school.

Pedrosa, 25, could not be reached. Her attorney, J.C. Planas, said his client did nothing wrong.

“She contacted my office, she told me the police wanted to speak with her, and I advised her to speak with them and cooperate fully,” said Planas, who served in the state House of Representatives with Bovo two years ago.