On February 26, 2004, at 2: 30 PM local time, two Chinese "diplomats"  drove through a guarded checkpoint at Los Alamos National Laboratory in New Mexico, at a high rate of speed, and went straight to a nuclear research area. The checkpoint they passed was a temporary one and could have been mistaken as a lab exit. The fast driving pair were intercepted by security personnel as their rental car was blocked by stoplight traffic. The two men were not  actually diplomats, but security agents working for the Chinese embassy.

When stopped, the two identified themselves as diplomats assigned to the Las Angeles Chinese Consulate. A search of the car didn't turn up anything, but odd discrepancies raised warning flags. Rental license plates are normally mounted on front and back of the vehicle, but the car had two licenses places taped together on the back. Nor had the two men requested or received clearance from the U.S. State Department to travel to New Mexico on February 26-27. Chinese diplomats are barred from traveling outside a specific zone surrounding the consulate unless the State Department gives prior permission. The two had flown to Albuquerque in the morning, and spent about an hour and a half in the Los Alamos area before running the checkpoint. They stayed overnight at Santa Fe, and returned to Los Angeles the next day. 

The Chinese have waged a persistent campaign to obtain U.S. nuclear weapons secrets and in the 1990s obtained a neutron bomb design developed at Lawrence Livermore Labs. Chinese espionage methods rely on many small efforts, not a few big operations. This particular incident has some people thinking it was more than just "two guys who got lost." Doug Mohney