John Pistole was sworn in as head of the TSA on Thursday.

Washington (CNN) - Former FBI Deputy Director John Pistole was sworn in as the new head of the Transportation Security Administration Thursday, concluding a lengthy search process in which two previous nominees withdrew from consideration amid allegations of improprieties.

The missteps left the agency - which includes the nation's 50,000 airport screeners, thousands of air marshals, and others - with an acting chief for almost a year and a half, a time marked by a series of transportation-related security scares, most notably the Christmas Day bombing attempt on an aircraft entering the United States.

Pistole was sworn in by Homeland Security Secretary Janet Napolitano during a rail security event at New York's Pennsylvania Station.

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