'Extremely Dangerous' Radioactive Material Stolen A truck packed with dangerous nuclear material, stolen south of our border. Our chief justice correspondent, pierre thomas, has been tracking this through the night. And, pierre, explain why officials are so worried about this hijacking. Today u.S. Authorities on the southern border are on heightened alert. They're concerned about the radioactive material stole at the mexican border. A struck stolen near mexico city is drawing international concern. It housed this medical device, used in the treatment of cancer patients. In it, cobalt 60 teletherapy, a radioactive material that can be dangerous if it's moved or the shielding of the device is damaged. If you have a large quantity, an entire truck of this cobolt 60, could you do other harm? That's the question at this point. Reporter: U.S. Officials are monitoring closely. The truck was stolen at a gas station just 35 miles outside of mexico city. It is unclear who stole the material. And if they know what they have. But even though the theft occurred hundreds of miles from the u.S. Border, there's a reason why the incident is drawing such intense scrutiny. U.S. Officials have long been concerned that stolen radioactive material could be used to make a so-called dirty bomb. Such a device could not cause a nuclear explosion. But the cobolt could release radioactive elements or something that could scare people. Could you figure out if you have a large quantity of cobolt 60, could you do something environmentally catastrophic? Reporter: U.S. Officials are working hard to track this theft. Just spoke to a senior official who said there's no reason to panic. But they're taking no chances. This material has been stolen before. Cannot create an explosion. But it can make people really sick. It can make people very sick. And again, the real concern is that beyond the medical issues, that you can really scare people if there was a release of this material. It's a terror weapon, more so than a huge, explosive weapon. On the search for it right now. Pierre thomas, thanks very much.