RDU INTERNATIONAL — Even with heightened security at

Raleigh-Durham International Airport

, a man pulled off an armed robbery at an office near the main parking lot last week.

Police say a gunman approached a parking supervisor in the office last Monday, took him to the back of the office and tied him up. An RDU spokeswoman says the gunman took some cash that was in a safe.

Officials say the man knew what he was looking for, and that two of the three people involved in the heist worked inside the airport. Those two have been arrested, and a third man being sought is identified as the gunman.

The robbery marks the second time this year that RDU parking service employees have been arrested on charges of stealing public funds, either by force or by deception.

The incident occurred outside the 300-foot security zone established by the FAA to protect travelers following the September 11 attacks.