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An outside law firm brought in by New Jersey Gov. Chris Christie to examine the bridge closure scandal reported Thursday that their investigation found the governor was not involved in the plot.

Released by former federal prosecutor Randy Mastro, the report relied on interviews with officials in the Christie administration, including the governor, and 250,000 documents.

"We found that Gov. Christie had no knowledge beforehand of this George Washington Bridge realignment idea," Mastro said at a news conference.

In the wake of the scandal, Christie had reached out in January to law firm Gibson, Dunn & Crutcher to help with an internal review.

The report comes out ahead of results from investigations by federal prosecutors and a special committee of state lawmakers. Some of the key figures would not cooperate with Mastro's investigation, leading Democrats to question the credibility of the report and its thoroughness.

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    A Democratic Party spokesman called the taxpayer-funded report an "expensive sham."

    But Mastro defended the report, saying his team was able to review a trove of documents, including emails and text messages among Christie, Lt. Gov. Kim Guadagno, top governor's office staff and former staffers. "We believe we have gotten to the truth or we wouldn't be reporting it," he said.

    He also said the lane closures were not reflective of the way the governor's office generally operates. "We found that this was the action of the few," he said. "This is not reflective of the whole."

    He said his team was sharing information with federal prosecutors.

    The September closure of lanes near the George Washington Bridge that caused four days of massive gridlock in the community of Fort Lee have become a major scandal for Christie, a possible 2016 Republican presidential contender. Christie said on a radio show Wednesday that the events will not affect his decisions about his political future.

    The report, issued at Mastro's New York law office, concludes that former Port Authority of New York and New Jersey official David Wildstein and ex-Christie aide Bridget Kelly were behind the closures and that they were targeting Fort Lee Mayor Mark Sokolich. But it did not conclude why they wanted to hurt the Democrat and said there was no evidence that it was because he refused to endorse Christie for re-election last year.

    The report says that Sokolich himself brought up the possibility of endorsing Christie but ultimately decided against it. The report says that even after that decision, the mayor remained on a list of Democrats whom Christie was considering appointing to various boards.

    Mastro said Wildstein seemed to have "bizarre political and personal animus" against a variety of people.

    Mastro said that Kelly, who did not cooperate with the report, tried to cover her tracks when Christie began asking what happened last year by asking a colleague to delete an email about the plot. But the other staffer retained the email anyway, the report says.

    Mastro also said that Wildstein suggested he mentioned traffic issues in Fort Lee to Christie at public event during the lane realignment. But he says Christie did not recall it being brought up and if it was, it would not have registered as significant to Christie -- something Christie has said before.

    The report also finds that a claim by Hoboken Mayor Dawn Zimmer, that Christie's administration told her that Superstorm Sandy would be tied to a private redevelopment plan, is "demonstrably false." A spokesman for Zimmer did not immediately return a call.

    The Associated Press contributed to this report.