[The son of the limo company owner at the center of the investigation was arrested.]

In 2001, a 45-year-old gas-station owner from Pakistan named Shahed Hussain walked into the Department of Motor Vehicles in Albany and obtained a driver’s license using fake documents for a would-be taxi driver who paid him $1,000.

Mr. Hussain was caught, faced federal charges and, to avoid deportation, began a secret career that led him to pose as a recruiter of terrorists.

He continued to run a series of businesses with his family, despite bankruptcy and legal issues — including, eventually, a limousine service that repeatedly ran afoul of state inspectors.

Now, Mr. Hussain’s improbable journey — from asylum-seeking immigrant to petty criminal to trusted ally of government prosecutors, has taken yet another turn. His complicated past is central to the investigation of the nation’s deadliest crash in years.