A box containing human heads was stolen from a parked freight company truck in Denver, officials said Saturday. The box was being transported for medical research purposes and Denver police are investigating the incident. Someone broke into the truck Thursday morning while it was parked in Denver’s Central Park neighborhood on Thursday morning, CBS Denver reported. The blue-and-white box was marked with a label that said “Exempt Human Specimen,” police said. A dolly was also stolen from the truck. “Pretty shocking,” one local resident told KDVR-TV. “I guess I don’t see too many strange things happening around here usually, but you know, you never know.” The incident comes just days after the Denver Police Department warned on Facebook that “vehicle-related crimes such as auto theft and theft from motor vehicle continue to be a problem in Denver.” No arrests had been made as of Saturday and investigators asked anyone who finds the box to call Metro Denver Crime Stoppers (720) 913-STOP (7867).