Juan Eibenschutz Hartman, head of the National Commission for Nuclear Security and Safeguards, said the container was open and investigators were unsure if any cobalt was missing, CNN reported. Radioactivity was detected around the container.
The International Atomic Energy Agency said Mexico notified it that the truck was stolen Monday in Tepojaco, near Mexico City. The agency said the material was being transported from a Tijuana hospital to a radioactive waste center.
Jaime Aguirre Gomez, deputy director of radiological security at the commission, said preliminary findings suggest the thieves did not know what they were getting into when they stole the truck, CNN said. But there are concerns because cobalt-60 can be used to make "dirty bombs."
Ernesto Morales, the prosecutor in the area where the theft occurred, said the driver and his assistant told investigators they had pulled in to a gas station to nap. Morales told CNN they reported being hijacked by a man who threatened them with a gun, telling them to turn over the keys.
The gunman and another man tied them up. They said they heard one of the men talking on a cell phone, telling someone "it's done," Morales said.