DENVER -- In a stunning admission, the city's manager of aviation said that there are thousands of airport security identification badges unaccounted for at Denver International Airport.

7NEWS Investigator John Ferrugia has been following the story.

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Airport officials issue a total of more than 20,000 employee security badges to airlines, contractors who work at the airport, and to concessionaires.

If even one is not accounted for, it is a major security risk, Ferrugia said.

DIA aviation director Bruce Baumgartner said that it was only last week when airport officials removed 3,000 airport badges from the security system. They were unaccounted for after current employees were told to renew their credentials.

"We have completed the project and the net result was that Thursday morning we invalidated all badges that had not been re-validated, and there were about 3,000 of those not re-issued," Baumgartner said.

That means that airport officials have no idea who has those badges, Ferrugia reported.

Some may be employees who have just forgotten to renew, or there might be hundreds of passes that were being held by employers like airlines, contractors, concessionaires, or employees who quit working at the airport up to two years ago, Ferrugia said.

Airport officials said that those companies who have employees at the airport are supposed to notify the Department of Aviation when an employee leaves or is fired.

But at this point, city officials have no idea whether that has happened, and have no system in place to check it.

So, now city aviation officials are now checking records to find out which employers have badges that are unaccounted for.

The bottom line is that for up to two years, there has been the potential for a huge security breach at DIA, Ferrugia reported.

Even though those badges are now de-activated, the question is: who in the aviation department is responsible?