NEW YORK (Reuters) - The mastermind of the Bridgegate lane closure scandal, which helped derail New Jersey Governor Chris Christie’s presidential ambitions, avoided a prison sentence on Wednesday, after U.S. prosecutors praised his help in their investigation.

David Wildstein, 55, a former executive at the Port Authority of New York and New Jersey and a high school classmate of Christie’s, provided the key evidence that led to the conviction of two Christie allies.

“Were it not for Mr. Wildstein’s cooperation, it is unlikely that we are even here today,” Assistant U.S. Attorney Lee Cortes told U.S. District Judge Susan Wigenton in federal court in Newark, New Jersey.

The judge sentenced Wildstein to three years of probation, noting that he was the only figure in the scandal to accept responsibility for his actions.

Wildstein concocted a scheme to shut down access lanes at the George Washington Bridge in September 2013, causing massive traffic jams as punishment for a local Democratic mayor who declined to support Christie’s gubernatorial re-election bid.

The bridge between New Jersey and New York City is the world’s busiest, according to the Port Authority, which oversees it.

Christie, who was never charged, has denied any involvement, despite Wildstein’s testimony that the governor was aware of the plot as it unfolded. The fallout damaged Christie’s unsuccessful 2016 bid for the Republican presidential nomination, and he is now saddled with record-low approval ratings in his final year as governor.

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Wildstein’s co-conspirators, former Christie aide Bridget Kelly and former Port Authority executive Bill Baroni, were found guilty after Wildstein’s testimony implicated Kelly, Baroni, Christie and other key Christie administration figures.

Kelly and Baroni were sentenced to 1-1/2 and two years in prison, respectively. They are free on bail while they appeal their convictions.

Wildstein said that he, like Kelly and Baroni, had fallen victim to a toxic atmosphere fostered by Christie.

“I admit to being a willing participant in a culture that was, upon reflection, disgusting,” he said. “Each of us put our faith and trust in a man that neither earned it or deserved it.”

It was Wildstein’s willingness to turn over incriminating messages to state legislators that ensured the scheme came to light, Cortes said. Those documents included an infamous email in which Kelly told Wildstein, “Time for some traffic problems in Fort Lee,” setting the plot in motion.

Kelly, Cortes said, had deleted that email along with others, leaving Wildstein as the only source of crucial information.