The tortoise and the thief, in Dubuque

(CBS/AP) DUBUQUE, Iowa - Iowa investigators want to know who took an 18-pound African leopard tortoise from an exhibit at a Dubuque museum. The animal was subsequently found alive in an elevator in the building, the National Mississippi River Museum & Aquarium.

KWWL-TV reports authorities believe the tortoise named Cashew was stolen, but that the thief then changed his stripes - or, perhaps, spots - and returned the animal.

The museum says a visitor found the tortoise on the elevator floor Thursday, apparently in good health, two days after Cashew was determined to be missing from an exhibit with a 4-foot glass wall.

Museum officials suspected she was taken as a prank or to sell.

They're reviewing surveillance video to try to figure out exactly what happened, and "who dunnit."