A truck carrying "extremely dangerous" radioactive material was found Wednesday close to the place where it was stolen in Mexico, authorities said. The cargo was found about half a mile from the container.
The vehicle was transporting radiotherapy equipment containing the radioactive isotope cobalt-60 from a hospital to a waste storage center, the International Atomic Energy Agency said.
"At the time the truck was stolen, the source was properly shielded," the IAEA said in a statement. "However, the source could be extremely dangerous to a person if removed from the shielding, or if it was damaged."
The thieves likely opened the container not knowing what it was carrying and burned themselves, Juan Eibenschutz, general director of Mexico's National Commission of Nuclear Security and Safeguards, told NBC News. The thieves are likely either dead or dying following the incident, Eibenschutz added.
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Officials have closed off the area where the radioactive material was found. They are conducting tests to determine when it is safe to approach it.
The vehicle is a 2.5-ton Volkswagen truck with an integrated crane. It was stolen on Monday at a gas station in Tepojaco, near Mexico City.
Mexico's federal, state, and local authorities were involved in a widespread and coordinated hunt for the vehicle across several states, the CNSNS said.
U.S. officials say it's not at all clear why it had been stolen, adding that there was no indication it had been taken for any criminal or terrorist purpose.
"It could be," one federal official said, "that whoever stole the truck had no idea what was inside and was more interested in getting a truck."
One law enforcement official says the radioactive material the truck was carrying is a thumb-sized amount of cobalt-60, used in medical treatments.
"It would be extremely dangerous to anyone who tried to grind it up for use in a dirty bomb," the official said.
The main concern of authorities was that the material in the stolen truck is dangerous to handle. In addition, it could also be used to make a radioactive dirty bomb, as could all similar materials used in medicine and industry.
At the same time, U.S. officials say cobalt-60 is among the materials that would be hardest to disperse over a wide area, assuming such a device could be made.
According to safety guidelines on the IAEA website, a "malevolent use of radioactive sources…could also cause significant social, psychological and economic impacts."
There also are many documented cases of people unwittingly stealing or acquiring radioactive material and then becoming ill or dying.
IAEA spokeswoman Gill Tudor told NBC News: "Such thefts are not uncommon, and the thieves do not necessarily know what they have in their possession in addition to the vehicle that may have been the original target.
"In some cases, for example, radioactive sources have ended up being sold as scrap, causing serious health consequences for people who unknowingly come into contact with it."
—By Pete Williams and Alexander Smith, NBC News