Kushal The Killer

Riddle 
Kushal is  living at  alone place. He own a shed which has been locked. The lock that has been placed on the door can be closed without a key but need the key to be opened.

    (Hint :The main hint here is that the lock can be closed without a key, so think about it and Kushal will get the answer.) The lock can be closed without a key. When Kushal were keeping the things inside the shed, the murderer took the lock hanging on the door and replaced it with an identical one. Kushal closed it as it did not require a key. When Kushal were gone, the murderer opened the new lock with his key, planted the body inside, replaced the lock with the original one again and locked it.