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ALBUQUERQUE, New Mexico (CNN) -- A criminal investigation is under way into how radioactive material ended up at a New Mexico fairground, police said Sunday.
No one was endangered by the chemicals that were found, said Lt. Juan Martinez, a spokesman for New Mexico State Police.
About 500 people were evacuated from the New Mexico State Fairgrounds Expo on Saturday evening as a precaution after low levels of radiation were detected, he said.
A Geiger counter registered the presence of radiation after two objects were discovered at the 236-acre fairground in the heart of Albuquerque, Martinez said.
One object originally thought to be a possible pipe bomb was later identified as a casing used to transport cesium, a radioactive element, he said.
There was some cesium present along with cobalt-57, a material used in the medical and plumbing industries, Martinez said. Cobalt-57 is a radioactive poison used in biological research, but it was in a condition well past its effective radioactive life and posed no danger, Martinez said.
The casing and the second object, a paint can, were found under a car parked near the fairground's fine arts building, Martinez said. One object was marked "nuclear" and the other, "cobalt," he said.
Many fairgoers were forced to leave their automobiles in the parking lot when the evacuation was announced.
"We were walking to the car and they made us leave and they said they had found something under a car," said Sheri Repahouski, who was attending a crafts fair.
She was among hundreds whose cars were still in the fair parking lot more than two hours after the evacuation. Buses arrived at the fairground to transport people to nearby Cesar Chavez Community Center, police said.
A bomb squad unit and hazardous materials teams searched the area for additional devices and worked to neutralize the items, which were found about 3:15 p.m., Martinez said.