The Bridgegate case against two former aides of the New Jersey governor, Chris Christie, neared its end on Friday as prosecutors argued that the traffic chaos caused by lane closures on the George Washington Bridge in 2013 was designed to punish a local mayor for withholding his endorsement of the governor’s re-election bid.

“You think any of this would have been done without the direct knowledge of participants?” asked prosecutor Lee Cortes. “No way … it was a cruel and callous scheme.”

Prosecutors claim the scheme was a direct response to Mayor Mark Sokolich of Fort Lee, a Democrat, who refused to endorse the Republican governor’s re-election bid. Fort Lee is on the New Jersey side of the bridge that connects the state with New York.

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As news of an alleged plot and cover-up surfaced in early 2014, Christie offered a meandering, 107-minute TV apology, denying any knowledge of the events and pronouncing himself “stunned by the abject stupidity” of his aides engaging in such a plan.

But the credibility of those assertions has been strained, if not shredded, by six weeks of testimony delivered by members of Christie’s “inner circle” that prosecutors described as a “coterie of cowards”.

Federal prosecutors produced a text sent by Bridget Anne Kelly, Christie’s former deputy chief of staff and one of the two defendants charged, during the press conference. “He just flat out lied,” Kelly texted.

As the case against Kelly and co-defendant Bill Baroni, Christie’s deputy executive director at the Port Authority that administers crossings to Manhattan, is prepared for jury deliberations, the one witness the court did not hear from is Christie himself.

Kelly testified that she talked to the governor twice about the lane closures while they were under way, including once when she passed along that Sokolich had asked whether the lanes were closed for “government retribution”.

Kelly said that David Wildstein, a former high-ranking official at the Port Authority and the admitted mastermind of the lane closure plot, told her in June 2013 that he was working with Port Authority engineers and police on a “traffic study”.

She also said there were explanations for emails and texts that prosecutors offered as evidence that she participated in the scheme that appears to have begun on 12 August 2013, when she received an email from Wildstein: “I have an issue to discuss with you, extraordinarily weird even by my standards.” Kelly then wrote to Wildstein: “Time for some traffic problems in Fort Lee.”

In Friday’s summations, Cortes argued Kelly’s words meant precisely that: “They were not about a traffic study. They are a direct view into minds of the participants.”

In another, infamous exchange, she’d replied “Is it wrong that I am smiling” after Wildstein described in an email how school buses had been caught in the traffic chaos. Kelly explained she was simply pleased that her colleague’s “traffic study” was progressing.

In a key passage, Wildstein, the government’s star witness, testified that he got approval for the scheme from Baroni and Kelly. He said Christie was told about the traffic in Fort Lee on the third day of the gridlock during a September 11 memorial event.

Facebook Twitter Pinterest Bill Baroni, arriving at the federal courthouse in Newark, is jointly accused with Bridget Anne Kelly. Photograph: Rich Schultz/AP

Wildstein said his job was to serve the interests of his only constituent – his former high school friend, Christie. “Being the bad cop when it was necessary to move something forward. It was my expectation that I would be tough.”

Baroni testified that Wildstein told Christie about the traffic congestion but denied knowledge of it. Mike DuHaime, one of Christie’s closest political advisers, also testified saying he told Christie in December 2013 that Kelly and campaign manager Bill Stepien knew about the lane closures.

But the presiding judge in the case, Susan D Wigenton, said prosecutors do not have to prove that defendants intended to punish Sokolich in order to convict on nine counts of conspiracy and fraud connected to the scheme and its cover-up.

Notwithstanding the outcome, the trial has been damaging for Christie as he was reportedly passed over as Donald Trump’s running mate in part because of the shadows thrown by Bridgegate.

The trial has also offered a fascinating glimpse into an administration that could effortlessly reward retribution. An email by Wildstein revealed in court said the Christie administration considered the Port Authority a “goody bag” to distribute favors, money and jobs.

Sokolich described how Christie aides first tried to win his re-election endorsement with gifts, including trips to the new, partially constructed World Trade Center, one of the flags that had flown over Ground Zero, and lengthy lunches at the governor’s mansion in Trenton.

But when Sokolich indicated he would not endorse the governor, the mood abruptly changed. Sokolich testified he had tried to reach Christie aides, including Baroni, but was stonewalled. Baroni later told jurors he had asked himself 1,000 times why he did not call the mayor back. “I listened to David Wildstein,” he said.

Sokolich said he was forced to conclude “the only plausible reason” for the closures “is someone is mad at me”.

Jurors will begin deliberations on Tuesday.