Somewhere far, far away, in the Kingdom of Puzzling, disaster has struck: the king's been assassinated! Here's the crime scene report:
The king was discovered dead in his royal bathroom with a single bullet hole in his chest. The guards on duty at the time claim he entered the bathroom, alone, approximately 15 minutes before he was discovered. The bathroom has only one door, which was not opened until after the king was already dead. It has no windows, vents, or any other ways in or out. Additionally, the bathroom is reinforced with steel walls several feet thick. The room was fully cleared prior to and immediately following the assassination, meaning nothing was out of the ordinary. No weapon was found except for a single, rather small bullet.
Clearly, investigators are quite puzzled about what could have gone down. How was the king assassinated?
Attributions: I created this puzzle, but it was loosely based off of a scene in a book. The solution is not the same as what happened in the book.
Bonus question: What book was this puzzle based off of?
Edit: I'd like to point out that there is one small detail that leads to a single, definitive answer.
Each of the answers so far have been flawed in some way, and fail to include this.
1. clearing of bathroom 2. guard inspection 3. king's entrance 4. king'death 5. discovery of the body 6. clearing of bathroom
or1.
and2.
inverted ? $\endgroup$