Kill now, report later

An couple spent a week in Honolulu for their 20th anniversary. They rented a cottage and roamed the island and enjoyed the beach. Two weeks after they came home, they called the police in Honolulu and told them that they had found a dead body in the bush behind the cottage they stayed. The police went there and found the corpse. However, the couple was not accused of reporting two weeks after they left. Why?