After a 16-month federal investigation into the George Washington Bridge lane closings scandal, a judge in New Jersey unsealed indictments against two people close to Gov. Chris Christie, outlining a conspiracy made with a third confidant to exact political vengeance against a mayor for not endorsing the governor’s re-election.

The United States attorney for New Jersey, Paul J. Fishman, announced the indictments at a news conference on Friday, breaking his long silence about a scandal that started as an inquiry into the cause of a traffic jam and has since led to a host of other investigations into the Christie administration, threatening the political future of one of the nation’s leading Republicans.

Mr. Fishman said that the conspirators “callously victimized” the citizens of Fort Lee, N.J., purposely scheduling the lane-closing plan to coincide with the first day of school. Then, he said, they sought to cover up the scheme with a “sham” story of a traffic study on the bridge to Manhattan. He said that there was evidence to suggest that using a traffic jam to exact revenge was discussed as far back as 2011.