(Carmen Natale)

David Samson, the chairman of the Port Authority of New York and New Jersey who came under scrutiny amid the Bridgegate investigations, resigned on Friday afternoon.

Gov. Chris Christie announced Samson’s departure at a press conference, describing it as part of a change in leadership that is necessary for reform of the bistate agency.

Samson, a name partner at Wolff & Samson in West Orange, N.J., issued a statement Friday saying he and Christie had discussed his resignation months ago. “The timing is now right, and I am confident that the Governor will put new leadership in place to address the many challenges ahead,” Samson said.

Christie said the resignation, which is effective immediately, had nothing to do with the ongoing investigations of last fall’s abrupt closure of local access lanes to the George Washington Bridge, which the Port Authority owns and operates.

Christie added that he persuaded Samson to stay on through his reelection and for the first months of his second administration. “He’s 74, and he’s tired,” Christie said.

Christie was asked about the fact that Samson refused to answer questions from Gibson, Dunn & Crutcher, the firm that the governor retained to investigate his administration’s possible complicity in the bridge lane closures.

“He explained that there were attorney-client privileges that he feared would be compromised,” Christie said. “I didn’t push it any further.”

One of the recommendations made by Gibson Dunn in its report of the investigation, released Thursday, was a restructuring of the Port Authority.

Christie said Samson called him early Friday and said he “completely supports” that recommendation and that it should “begin with new leadership.”

Christie said he has not made a decision on a replacement for Samson.

Also on Friday, Christie said he has not decided whether to nominate his chief of staff, Kevin O’Dowd, to become attorney general, as he had announced his intention to do last December.

O’Dowd was among many of Christie’s close advisors subpoenaed by the New Jersey Legislative Select Committee in January and likely would have faced intense questioning by the Senate Judiciary Committee.

Christie was asked at the conference why a push was not made earlier to get the nomination through.

Christie said he did not think it would have been appropriate to have O’Dowd’s nomination considered at least until Gibson Dunn issued its report. The firm’s report cleared O’Dowd, along with Christie and most of his staff.

“My support of Kevin has never wavered,” Christie said, adding that he would “sit down” with O’Dowd soon and decide what course to take. “We’ll see if he still wants to do this,” he said.

Christie also defended his decision to retain Gibson Dunn, and partner Randy Mastro, who has a close relationship with former New York City Mayor Rudy Giuliani, a Christie ally.

Christie said it was important to retain a “significant” law firm with the resources to conduct an investigation, and due to his tenure as U.S. attorney for New Jersey, there are few large firms with whom he does not have some relationship. “No matter who I chose, questions were going to be asked,” he said.

Christie defended the conclusion in the report, and how it was conducted. “They [Mastro and his team] would not give up their reputations to do some slip-shod job for me,” he said.

Christie said he could not say how much the state has paid for Gibson Dunn’s 10-week investigation, and refuted estimates by some media organizations that the firm has been paid at least $1 million.

“If you want to have a search for the truth, you need to get lawyers to help you shepherd it through,” he said. “That means they get paid.”

He referred questions about the bills to the Attorney General’s office, which said Friday that the firm has not yet submitted any bills.

The governor was also asked whether the on-going investigations into the lane closures, as well as other investigations into his doling out of federal aid to Hurricane Sandy recovery efforts, would affect his thinking on whether to seek the Republican nomination for president in 2016. He said it would not.

Christie said there will be two questions he will have to answer: Is running for president in his and his family’s best interests, and does he have something “unique and particular” to offer?

“If the answer to both of those is yes, I will seek that office,” he said. If the answer to either is no, he said he would not run for president.

Christie said he did not know of the motive behind the decision to close the bridge’s local access lanes from Sept. 9 until Sept. 13. The closures were orchestrated by Christie’s former deputy chief of staff, Bridget Kelly, and the Port Authority’s director of interstate projects, David Wildstein.

The commonly held belief is that the two concocted the scheme to get back at Democratic Fort Lee Mayor Mark Sokolich after he declined to endorse Christie for reelection. Kelly and Christie’s former campaign manager, Bill Stepien, who was told about what was occurring through emails and texts, have invoked their Fifth Amendment rights and have refused to cooperate with the investigations.

“I don’t know if we’ll ever know” the motive, Christie said. “It mystifies me on every level as to why this was done.”

Assemblymen John Wisniewski, D-Middlesex, and Sen. Loretta Weinberg, D-Bergen, the co-chairs of the Legislature’s committee investigating the closures, said Gibson Dunn’s findings are far from conclusive.

“Lawyers hired by and paid by the Christie administration itself to investigate the governor’s office who then say the governor and most of his office did nothing wrong will not be the final word on this matter,” they said in a joint statement released Thursday. “The people of New Jersey need a full accounting of what happened. This review has deficiencies that raise questions about a lack of objectivity and thoroughness.

“We will continue to pursue our investigation wherever the facts lead. We want a full accounting of the lane closings and any related abuses of power and what can be done to ensure this doesn’t happen again,” they said.

Contact the reporter at mbooth@alm.com.