"This is very, very dangerous," said Daniel E. Payne, head of the Defense Security Service, a federal office that oversees the granting of temporary clearances.

Payne said roughly 100,000 people hold interim clearances while working for companies with Defense Department contracts or at 13,000 cleared facilities and plants around the country and as they await a full comprehensive background investigation.

"I've got murderers who have access to classified information. I have rapists. I have pedophiles. I have people involved in child porn," Payne said. "This is the risk we are taking."

Payne spoke on a panel about the backlog in security clearances at the Intelligence & National Security Summit in Washington.

The backlog "grew precipitously" in 2015 and 2016, and stands at near record levels today, said Charles S. Phalen, director of the National Background Investigations Bureau, a federal service provider under the Office of Personnel Management.

The backlog encompasses roughly 700,000 cases, but only 300,000 or so people are seeking a first-time clearance to enter government service, Phalen said. The remainder may be federal employees or contractors seeking a periodic renewal of a security clearance or a change in their clearance level, he added. They stay in federal jobs.

Payne, a career counterintelligence officer with the CIA, said the concerns about interim clearances only affect the Defense Department and its associated industrial base, not the nation's intelligence agencies, where temporary clearances are never granted.

"I grant the interim clearances for the DOD. I also take the interim clearances away," Payne told a reporter after the panel ended. Asked how many cases his office had discovered of people with a murder in their background, he said: "It's more than several. I would say less than a dozen."

One case happened just a month ago when a man with an interim clearance got in an argument at a bar. "He pulls out a gun and shoots them in the face and kills them," Payne said.

Applicants obtain interim clearances after filling out a lengthy government form, known as an SF-86, and undergoing a credit check and an initial FBI background check.