June 28, 2012  -- Internal emails have revealed repeated, potentially dangerous security lapses at one of the nation's top bio-terror labs that houses deadly biological agents like anthrax and the SARS virus.

The emails from the Centers for Disease Control, first reported by USA Today and confirmed today by ABC News, describe multiple instances between 2009 and 2010 of doors within a supposedly secure facility in Atlanta being left unlocked, potentially allowing unauthorized access to the deadly strains. In at least one instance, someone without the proper security clearance was found in a restricted area.

"We are dealing with nasty agents that we need to have maximum containment," said Najmedin Meshkati, professor of engineering at the University of Southern California. "If they get released or discharged from that facility, it could be problematic."

One official said that while walking through a high-security area, he found two doors unlocked and said, "it has become a common failure point," according to the emails.

CDC officials told ABC News the public was never at risk and the government agency has addressed the concerns at the Atlanta lab. A spokesperson for the agency told USA Today the doors were just one layer of security at the labs and it would still be "close to impossible" for any intruders to get their hands on the dangerous microbes.

The CDC is in charge of its own security, an internal review system that Dr. Richard Besser, one of the Centers' previous heads and current ABC News chief medical editor, said needs to change.

"I think it's clear that no laboratory should have oversight of itself," he said. "You need an independent group looking at them and I think the CDC would go for that."

Earlier this month, USA Today reported the same facility was having difficulties with its air flow system, which is designed to keep potentially dangerous air from escaping into "clean" areas.

Following the air flow problem reports, the Congressional leaders in the House Energy and Commerce Committee launched an investigation into the safety measures at the $214 million facility.

ABC News' Lee Ferran contributed to this report.