The three then made up a cover story: They would say that they were doing a traffic study so that unwitting Port Authority staff members would go along with the plan, making it appear to be legitimate. That would require some planning and the involvement of unwitting participants.

Mr. Wildstein had a traffic engineer prepare several configurations; Mr. Baroni and Ms. Kelly agreed that the one that funneled three access lanes into a single one would inflict the worst punishment on the mayor, by creating the most severe traffic backup on the streets of Fort Lee. They would steer that lane to a tollbooth that accepted cash as well as E-ZPass; there would be no access to the E-ZPass-only lane that offered a faster commute.

They were ready in August, but Mr. Baroni recommended waiting. After all, traffic tended to be lighter in summer; “the punitive impact would be lessened,” the indictment says. They bided their time. They agreed: They would do it the first day of school, Monday, Sept. 9, 2013, in order to “intensify Mayor Sokolich’s punishment.”

They agreed not to tell him, or any officials in Fort Lee, so that there would be no time to prepare. It would also, the indictment says, “keep Fort Lee residents and G.W.B. commuters from altering their routes.”