MAYS LANDING, N.J. — Atlantic City Mayor Don Guardian stood outside the Atlantic County Clerk's Office on Friday afternoon and said this coming Tuesday's election has already been compromised by what he alleges is a fraudulent vote-by-mail and messenger-ballot scheme being carried out on behalf of his opponent, Democratic Councilman Frank Gilliam.

"People are very upset about trying to have their votes bought and about being taken advantage of by the people in the white vans," the Republican incumbent said. "All we're asking for is a fair and just election. Stop the dead people from voting in Atlantic City."

The news conference was called nearly a week after two private detectives hired by the mayor's campaign sent an informant, Rodney Cotton, 51, wearing a recording device, into the Gilliam for Mayor headquarters, where he met up with Craig Callaway, a well-known Democratic operative who has quarterbacked an exhaustive vote-by-mail campaign. He said he was paid $30 to be a messenger for a voter, but turned the ballot over to Callaway.

Callaway, who walked in and out of the clerk's office as the mayor spoke Friday afternoon, and crossed the street to check with the Superintendent of Elections Office at one point, called it "the biggest distraction and sideshow in the history of Atlantic County," and has denied doing anything illegal. Callaway also was active during the 2013 election.

Gilliam has denied any connection with the Callaway operation and called the mayor's actions an "act of desperation."

The sting operation, observed by a reporter and reported in the Inquirer this week, has prompted the mayor's campaign to meet with the county prosecutor and  attempt to challenge the ballots ahead of Tuesday's election.

The Board of Elections, which met Thursday evening to begin checking mail-in ballots, said the bulk of the ballots would be processed by staff on Monday without challengers present.

During the meeting, the commissioners debated and then discarded a ballot belonging to a woman in Linwood who they said had died in 2015.

On Friday, Guardian said his campaign has found numerous voters registered to vacant lots and abandoned buildings, and that 2,000 sample ballots were returned to the clerk's office. His detectives have interviewed a number of voters who say they were paid $30 to vote the Democratic line. He gave out thumb drives containing audio, video, and written interviews and reports from his detectives.

"All we're asking is to check the people who voted early against the people whose ballots were sent back," Guardian said.

Once the ballots are separated from the envelopes with the voter's name and address, it is impossible to challenge them, he acknowledged. The mayor's campaign had been contemplating legal action, but none had been taken as of Friday afternoon.

Cotton, who was brought to Guardian's news conference by the two private detectives hired by the mayor's campaign, told reporters he became an informant "on his own accord," and was not influenced by any of the mayor's supporters.

"I am here to represent the invisible, the homeless in Atlantic City, the brothers and sisters who are being taken advantage of this election process," he said.  "This just doesn't sit well with me, that's the reason I am here."

The county prosecutor, the state Attorney General's Office, and the Department of Law have declined to comment.