The US attorney in New Jersey is set to open an inquiry into recent controversial bridge lane closures, which critics say were engineered by New Jersey Governor Chris Christie's staff for political retribution, The New York Times reported.
The newspaper gave no further details.
Christie is a possible Republican contender for the 2016 White House race.
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Harrow pupil Archie Lloyd was celebrating the end of his exams in Crete when he was knocked to the ground in August 2015.
The incident is not believed to be terror-related, British Transport Police said.
The royal couple have been in the US to mark the 300th anniversary of the foundings of New Orleans and San Antonio.