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The Key the Intruder Placed (illustration)
FILE No.139Unsolved

The Key the Intruder Placed

Difficulty ★★☆about 5 minLocked RoomPoints in timeKeys
The caretaker, looking in from outside the window, says there was no key on the desk. After the door was broken down, a key was on the desk.

Case Record

The master of the house was found collapsed in his study. The door was locked from the inside, with no sign that anyone had come or gone. Only the secretary holds the spare key to the study.

The mansion's caretaker looked into the study through a window from the garden and said, "There was no key on the desk." (The caretaker has good eyesight, the desk is 2 meters from the window, and he took a photograph right after looking.) After that, the secretary led the way and broke the door down with his body, followed by the doctor and the driver. After they entered, the study key was on the desk.

Your question

When, and by whom, was the study key placed on the desk?

Case Files

Diagram

Until the study key appeared on the desk1) Caretaker looks through the window: no key on the desk (2 m,photographed)2) The secretary breaks the door down first; the doctor and driverfollow3) After they enter, the key is on the deskOnly the secretary has the spare key.
Diagram

Hints

If you get stuck, open the hints one at a time, in order.

Open hint 1

Did the caretaker look before or after the door was broken?

Open hint 2

Who holds the study key?

Open hint 3

Before the door was broken, who could enter the room?

Solve It

Your question

When, and by whom, was the study key placed on the desk?

Choose the answer closest to the truth.

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The Truth

After the door was broken down, the secretary, who holds the spare key, placed it

The answer is "After the door was broken down, the secretary, who holds the spare key, placed it."

The caretaker has good eyesight, was close, and there is a photograph. A "misjudgment" is unlikely. So someone must have placed it after the caretaker looked.

Before the door was broken, no one could enter, and those who entered afterward were the secretary, the doctor, and the driver. Only the secretary holds a key to the study, so the one who could place the key is the secretary.

Who could have placed the keyWhenWho could enterKeyBefore the doorwas brokenNobody (locked frominside)Cannot be placedAfter it wasbrokenSecretary, doctor, driverOnly the secretaryhas the keyAnswer: the secretary placed it after the door was broken down.
Diagram of the solution

Key Points

  • Separate "when it was seen" from "when the key was there"
  • Check who holds the key
  • Also doubt the movements after the door was broken

Why people get fooled

Because the fact that "the key was in the room" makes you think it was there from the start.

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