Apparently, those who bought the guns are residents of Colorado. They bought the guns in AZ. It is illegal to buy a long gun in a state in which you are not a resident, except from a licensed dealer, at his licensed premises. It is illegal to buy a handgun, from anyone, in a state in which you are not a resident.
They bought a handgun and several long guns from a non-licensee, and then took them back to CO, also crimes under Fed law.