CARIBOU, Maine — Officers process narcotics evidence in a small closet where they store paper towels. Locked ammunition and case files are stashed where there’s room, often in the same spaces as housekeeping items and office paperwork. Mold is growing on the walls in the garage, and rain is damaging rooms inside the police station. The 80-year-old Caribou police station is cramped, and the department wants a new one, but the $10 million price tag has some city officials nervous about burdening taxpayers.