You are living at you place alone. You 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. You collected some old stuff and decided to keep it in the shed. After keeping the things, you locked it back. The next day, the police found a dead body inside the shed. As you are the only one living in your house, the police has nothing else to believe than you are the murderer. But you have not committed any crime.
There is a way the murder would have happened. Can you find that way and tell the police so you are not sentenced for the crime you did not commit?
The lock can be closed without a key.
When you were keeping the things inside the shed, the murderer took the lock hanging on the door and replaced it with an identical one. You closed it as it did not require a key. When you 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.