William John Scott is a freshman at Drew University. He studies political science. He plays defense on the lacrosse team. He describes himself on Facebook as a night person who likes to party.

But federal prosecutors say he is something else: a busy archives thief who stole famous letters written by a founder of the United Methodist Church and world leaders, including Abraham Lincoln and Madame Chiang Kai-Shek.

Mr. Scott pilfered the letters while working part time at the university archives, the prosecutors said. He sold some of them for thousands of dollars, and left others sitting in a dresser drawer, where F.B.I. agents found them after executing a search warrant of his dorm room on Saturday. (On Facebook, Mr. Scott says he likes to keep the room “not a complete mess.”)

Mr. Scott was arrested on Sunday as the bus bringing his lacrosse team back from spring break rolled into Drew’s campus in Madison, N.J.

“He looked utterly surprised, like we were,” said Tyler Morse, a junior on the team who saw Mr. Scott escorted off the bus by the university’s head of public safety, into the car of F.B.I. agents....