Rep. Darrell E. Issa, California Republican and chairman of the Oversight and Government Reform Committee, said his staffers have come across verbal and written policies from the Office of Personnel Management that indicate the security clearance process was short-circuited in the case of Aaron Alexis, the Navy Yard shooter.

But Mr. Issa says OPM is refusing to turn over those documents and allowing them to be viewed only behind closed doors. If he doesn’t have the documents by noon Thursday, he said, he will issue a subpoena.

Mr. Issa said he thinks the agency is trying to protect itself from embarrassment from questions about the clearance process for Alexis and for Edward Snowden, the former contractor whose leaks have exposed some of the government’s most secret spy programs.

“These policies include the failure to secure arrest records that would have alerted federal officials to his violent past,” Mr. Issa wrote in a letter, obtained by The Washington Times, which was sent Wednesday to OPM Director Katherine Archuleta. “Perhaps most disconcerting, though, is OPM’s indifference to obtaining all the relevant information about individuals under review for a security clearance.”