Mr. Schulman did not respond to requests for comment. His lawyer, Robert G. Del Greco Jr., told The Pittsburgh Post-Gazette that his client was a “titan” in the book community. “The complaint sets forth serious allegations, and we are treating them as such,” he said.

The partnership between Mr. Priore and Mr. Schulman began in the late 1990s, according to an affidavit filed by the Allegheny County District Attorney’s Office, which investigated the case.

Mr. Priore told the authorities that he approached Mr. Schulman about selling some items in the library, but that Mr. Schulman later “goaded” him on.

Mr. Priore was the sole archivist for the collection of rare books, maps and other items at the Carnegie Library of Pittsburgh, the city’s public library system. He oversaw about 30,000 items in the collection and controlled who had access to it, the affidavit said.

Mr. Schulman and his wife own Caliban Book Shop, a block or so from the library, records show. He dealt in rare books, and was listed as a member of the Antiquarian Booksellers’ Association of America.

Over the years, Mr. Priore told the authorities, he removed items from the library — sometimes he used an X-acto knife to remove a part of a book, and other times he simply carried out a whole book or map — and dropped them off at Caliban Book Shop on his way home from work.

Mr. Schulman paid the archivist up front, records show, and then sold many of the items, including some to major book dealers.