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As part of an expanding investigation in the sex trafficking case against Jeffrey Epstein, federal prosecutors and the F.B.I. are trying to determine who traveled on the financier’s private planes in recent years, three people with knowledge of the matter have said.

Shortly after Mr. Epstein’s arrest on July 6, prosecutors in Manhattan issued federal grand jury subpoenas to two of his longtime pilots, according to these people, who spoke on the condition of anonymity because they were not authorized to discuss the inquiry.

The subpoenas sought passenger lists, flight logs and the personal notes the pilots had maintained, going back as far as they have records, the people said.

“They’re looking for flight logs, passenger manifests and anything that indicates who was on the plane,” one of the people said.