NEWARK, N.J. (Reuters) - New Jersey Governor Chris Christie was aware of a politically motivated scheme to close lanes at the George Washington Bridge in 2013 as it was unfolding, a key prosecution witness testified on Tuesday at the criminal trial of two former Christie associates.

New Jersey Governor Chris Christie enters the debate hall before the first U.S. presidential debate between Republican U.S. presidential nominee Donald Trump Democratic U.S. presidential nominee Hillary Clinton at Hofstra University in Hempstead, New York, U.S., September 26, 2016. REUTERS/Lucas Jackson

David Wildstein, a former executive at the Port Authority of New York and New Jersey who masterminded the plot, told jurors in Newark federal court that he and Bill Baroni, another Port Authority executive, discussed the lane closure with Christie before a memorial service marking the 12th anniversary of the Sept. 11, 2001, attacks at the World Trade Center.

The testimony marked the first specific evidence federal prosecutors have presented to back their contention that the Republican governor knew at the time about the scandal known as “Bridgegate,” despite his repeated denials.

Baroni and Christie’s former deputy chief of staff, Bridget Kelly, are charged with fraud and other crimes for allegedly orchestrating the September 2013 closure of access lanes at the bridge in Fort Lee, New Jersey, to punish the town’s Democratic mayor for refusing to endorse Christie’s re-election bid.

“Mr. Baroni said, ‘Governor, I have to tell you, there’s a tremendous amount of traffic in Fort Lee this morning,’” Wildstein testified, adding that Baroni was using a sarcastic tone.

Baroni also said the mayor, Mark Sokolich, was “very frustrated” that his calls to the Port Authority were being ignored.

“Governor Christie responded by saying, ‘I would imagine that he wouldn’t be getting his phone calls returned,’” Wildstein said.

Prosecutors showed jurors a series of photographs depicting the three men laughing at the site that morning, which was the third day of the weeklong lane closures.

Christie has not been charged with wrongdoing. Wildstein pleaded guilty to two counts of conspiracy and agreed to cooperate with prosecutors.

At an unrelated news conference in Trenton, New Jersey, Christie reiterated that he was never made aware of the scheme.

“I had no knowledge prior to, or during, these lane realignments. I had no role in authorizing it. I had no knowledge of it,” he said.

The scandal helped torpedo Christie’s White House run, undercutting his bipartisan image.

Since taking the witness stand Friday, Wildstein has described coordinated efforts by Christie’s office to use the Port Authority’s power to punish local officials who failed to get behind his re-election campaign.

Another such official, Mayor Steven Fulop of Jersey City, had meetings with executives from the Port Authority and other state agencies canceled after he declined to endorse, Wildstein testified.

At the same Sept. 11 event, then-Port Authority Chairman David Samson joined the three men and told Christie that Fulop was trying to reschedule a meeting, according to Wildstein.

“Governor Christie said, ‘No, no meetings with Mayor Fulop,’” Wildstein testified.

Samson, a close ally of Christie’s, had also been informed of the lane closures, Wildstein said. He pleaded guilty in July to an unrelated scheme in which he used his power to coerce United Airlines into reinstating a discontinued flight between Newark and South Carolina, near where he owned a vacation home.

At one point, Sokolich texted Baroni to say children were trapped on schoolbuses in the gridlock and practically begging for help.

“Is it wrong that I’m smiling?” Kelly texted Wildstein, who told the jury that the conspirators chose the first day of school for the closures to maximize traffic.

“They are the children of Buono voters,” Wildstein replied, referring to Christie’s Democratic opponent.