Chris Christie, the scandal-hit governor of New Jersey, embarked upon a full-throated attempt to save his shattered reputation on Thursday, firing the aide at the heart of a conspiracy to cause traffic chaos near a town controlled by a political opponent, and issuing profuse and repeated apologies.

In a 115-minute press conference from the governor’s office in Trenton, New Jersey, Christie said a top aide had lied to him about her involvement in the now notorious closure of traffic lanes on a bridge linking the state with New York City last September. He also said he had terminated his association with a senior Republican who had led his campaign for re-election in November.

Christie apologised to the people of New Jersey, and specifically to residents of Fort Lee, a small town in the shadow of the George Washington bridge that was thrown in chaos over four days of lane closures. The governor said he was “embarrassed and humiliated by the conduct of some of the people on my team”. Email exchanges between members of his inner circle, made public on Wednesday, had revealed behaviour he described as “stupid” and “deceitful”.

He told reporters: “I am heartbroken that someone I allowed in my inner circle for last five years betrayed my trust. I would never have come out four weeks ago and made a joke about these lane closures had I known that anyone in my staff had been so stupid to have anything to do with this and so deceitful,” he said, referring to his quip on 2 December that he had personally laid out the traffic cones.

Before the lane closures were ordered, the Democratic mayor of Fort Lee, Mark Sokolich, had declined to endorse Christie for re-election, incurring the spite of members of the Republican governor’s inner team. Christie went to Fort Lee on Thursday afternoon to apologise face-to-face to the mayor and to its residents.

In his remarks, Christie tried to lance the political boil that now threatens to poison his political future. The most caustic aspect of the swelling scandal is the impression left that the governor, who has been tipped as a frontrunner in the 2016 race for Republican presidential candidate, was a partisan bully.

“I am who I am, but I am not a bully,” he stated, trying to address that mounting criticism in trademark head-on fashion. Later, he went back on the theme, saying: “I have a very blunt direct personality and I understand why some people characterise that as bullying. But it’s not that.”

As he spoke, the US attorney in New Jersey, Paul Fishman, said he was "reviewing the matter to determine whether a federal law was implicated". The state legislature is also investigating.

Though Christie said on several occasions at the press conference that he accepted full responsibility for the mistakes committed by his team as chief executive of this state, implicit in his statement was the message that he himself was blameless. At most, he accepted that he might have been “naive” to have trusted some of his senior people.

Christie insisted repeatedly that he had no knowledge of the involvement of his top advisers in the decision to close the lanes, thus causing a major traffic snarl up in Fort Lee that delayed emergency vehicles and might even be implicated in the death of a 91-year-old woman . The first he learned that any members of his staff had been involved had been at 8.50am on Wednesday when news of the emails broke. At 9am on Thursday, he said, he dismissed Bridget Kelly, one of his three deputy chiefs of staff. " I was blindsided," Christie said.

The governor pulled no punches in his portrayal of Kelly, who was revealed in the emails to be an instigator of the lane closures. In an email to David Wildstein, a Christie appointee on the Port Authority , the organisation that controls the bridge, she wrote: “Time for some traffic problems in Fort Lee”. Wildstein replied: "Got it."

He said Kelly’s emails had made clear she had lied to him, and that she had acted towards the people of Fort Lee in a “completely callous and indifferent way”. Asked whether he had asked Kelly to explain her actions, he said he had not talked to her, adding: “Frankly, I’m not interested in any explanation at this point.”

The governor also said that he had forced Bill Stepien, his re-election campaign manager, to withdraw as chairman of the New Jersey Republican party and to stand down as a consultant to the Republican governors association, which Christie leads. in the emails called the Fort Lee mayor “an idiot”. The move makes Stepien the most high-profile casualty so far of what has been dubbed the “BridgeGate” affair, and brings the total number of Christie’s people forced to resign in the wake of it to four.

At a committee hearing at the New Jersey assembly on Thursday, Wildstein repeatedly refused to answer questions about the affair, asserting his right to remain silent under the fifth amendment to the US constitution. Wildstein refused to say where he previously worked, would not identify emails or redactions, and his lawyer said he would assert the right to remain silent to all questions.

The George Washington bridge toll booths are pictured in Fort Lee, New Jersey on 9 January 2014. Photograph: Carlo Allegri/Reuters Photograph: CARLO ALLEGRI/REUTERS

In addressing the media so fulsomely – inviting sarcastic tweets that he was trying to filibuster his way out of the crisis – Christie was gambling that his characteristic combination of straight talk and “man-on-the-street” bluster would see him through the scandal. But he remains in deep political water, especially with regard to his presidential ambitions.

Already, the vultures are circling. The Democratic party, both in New Jersey and nationally, have run with the bullying theme. The Republican right, which harbours doubts over whether Christie is a true conservative, has also pounced, with influential figures such as the talk-show host Rush Limbaugh saying the episode showed that he engaged in political “payback”.

Christie is particularly vunlerable to any further eeking out of information about “BridgeGate” or any other evidence that he or his team tried to strong-arm other politicians in the state. Earlier this week, the mayor of Jersey City, Steven Fulop, complained that the governor’s office had tried to disrupt his plans for pension reform in retribution for his refusal to endorse Christie last year.

Christie denied any vendetta against Fulop, but said he was unable to assure the public that there were no more revelations concerning the scandal to come. He said that the last 36 hours had taught him that he needed to be “much more circumspect” in what he said.