WASHINGTON — A National Security Agency employee has resigned from his job after admitting to FBI investigators that he allowed Edward Snowden, then an NSA contractor, to use his personal computer credentials to gain access to classified information, according to an agency memo.

The unidentified employee was not aware that Snowden intended to obtain classified material for the purposes of disclosure, said the memo, which was first reported by NBC News.

The employee is one of three people who have been under investigation for their unwitting involvement in Snowden’s effort to remove the material in what may be the largest breach of classified information in history. None was accused of collusion, said a senior U.S. official familiar with the investigation. “It’s a violation of procedures . . . but no ‘Hey, let’s conspire with him to steal information,’ ” said the official, who spoke on the condition of anonymity because the investigation is ongoing.

The employee who resigned, a civilian, had his security clearance revoked in November and was notified of a proposal to fire him. He resigned Jan. 10, said the memo, which was addressed to the staff directors of the House Judiciary Committee.

The two other people, a U.S. military member and a contractor, had their access to NSA facilities and material revoked in August, the memo said. They all worked at a regional NSA facility in Hawaii.