NEWARK, N.J. — Republican Gov. Chris Christie approved of a traffic study on the George Washington Bridge, his former deputy chief of staff testified Friday in her criminal trial, but federal prosecutors say it was actually a cover story for a political payback scheme designed to cause traffic jams.

After a conversation with Christie, Bridget Kelly sent an email that read “time for some traffic problems” to David Wildstein, the self-described mastermind of the plot.

Kelly is accused of plotting with Wildstein and another former Christie ally to close lanes on the bridge, which connects Fort Lee and New York City, as revenge against Fort Lee’s Democratic mayor, who wouldn’t endorse Christie’s re-election effort in 2013.

Her comments at trial that Christie signed off on the traffic study in August 2013, a month before the closures began, are the latest testimony indicating Christie knew more about the closures than he let on in the months afterward.

Christie’s spokesman said in a statement Friday night the governor had “no knowledge prior to or during these lane re-alignment” and “no role in authorizing them.” Spokesman Brian Murray said anything “said to the contrary is simply untrue.”

The scandal developed just after Christie won re-election handily and as his national political profile was rising. It ultimately weighed down his presidential campaign, which fizzled in the primary season after a poor showing in New Hampshire.

Also Friday, one of Christie’s top political advisers, Mike DuHaime, testified he told Christie ahead of a December 2013 news conference that Kelly and his campaign manager, Bill Stepien, knew about the lane closures. Christie then told reporters no one in his administration other than Wildstein knew about them.

Wildstein, a former Port Authority of New York and New Jersey staffer and high school classmate of Christie’s, previously pleaded guilty in the case and is the prosecution’s key witness. Wildstein has said the traffic study was just a cover story.

Kelly maintained Friday she believed the lane closings, on one of the world’s busiest bridges, to be part of a Port Authority traffic study and said they weren’t done for political retribution. She’s on trial along with former Port Authority executive Bill Baroni. They have pleaded not guilty and have said the government has twisted federal law to turn their actions into crimes.

The release of the “traffic problems” email was what brought the scandal into full public view and led to Christie firing Kelly and Stepien.

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