After a move to New Jersey, Sayfullo Saipov eventually settled in Paterson, N.J., and began driving for Uber. Federal authorities said he had come to their attention as a result of an unrelated investigation, but it was not clear whether that was because he was a friend, an associate, or a family member of someone under scrutiny or because he had been the focus of an investigation.

Saipov had earned a green card, according to a law enforcement official who spoke under the condition of anonymity because the investigation was proceeding, and had entered the country through Kennedy International Airport. An Uber official said Saipov had passed the company’s background check.

• Terror suspect Saipov passed Uber checks.