Mexico City (CNN) -- A week after the heist of a truck carrying radioactive material sent Mexican police scrambling, five suspects are behind bars.
Jose Luis Manjarrez, a spokesman for Mexico's Attorney General's Office, said Monday that five men who are suspects in the truck's theft will be held for up to 40 days while authorities investigate.
A minor was also detained in the case, Manjarrez said, but he was later set free and will be treated as a witness.
The six people were taken into custody after they were released Friday from a Mexican hospital, where they tested negative for radiation poisoning.
Investigators said the truck, which had been carrying cobalt-60 from a hospital to a disposal site, was stolen last Monday, prompting Mexican officials and the International Atomic Energy Agency to send out an alert.
Authorities have said the thieves may not have known they were taking a vehicle with radioactive cargo.
Investigators found the stolen truck Wednesday in Hueypoxtla, Mexico, about 40 kilometers (25 miles) from where it was taken. They also found the opened container that had been holding the radioactive cobalt nearby.
Since then, they've been working to clean up the area and contain it.
Authorities have said they've recovered all of the potentially deadly substance, which can be used to make dirty bombs but is also used for medical purposes.
Health officials said Friday that residents of Hueypoxtla and surrounding areas don't face any significant health risks due to the material, assuming they didn't contact it directly.
CNN's Catherine E. Shoichet, Nick Parker, Greg Botelho and Rafael Romo contributed to this report.