日本語
The Entrance Door with the Chain On (illustration)
FILE No.48Unsolved

The Entrance Door with the Chain On

Difficulty ★★☆about 5 minLocked RoomLocked roomTools
The door chain on the entrance was set from inside. How did the culprit come and go from the room where the body was found?

Case Record

An office worker named Kono was found dead in an apartment. The manager tried to enter with a spare key, but the front door would not open because the door chain was on. He had no choice but to cut the chain and go in.

All the windows were shut. The balcony is on the second floor, with no foothold and no sign of climbing.

However, on the upper part of the door frame on the outside, a small rubber band had snapped and fallen. Near the chain’s fitting there was a thin mark, as if rubbed by a rubber band.

Kono’s acquaintance was known for being good with his hands.

Your question

How did the culprit set the door chain from outside?

Case Files

Evidence

Diagram

Around the doorItemObservationDoor chainSet from insideOuter frameOne rubber band, snapped and fallenChain fittingThin rubbed mark nearbyWindowsAll shut; no foothold on the balcony
Diagram

Timeline

  1. Kono dies in his room.
  2. The manager tries to enter with a spare key, but the chain holds the door.

Hints

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

Open hint 1

What small object had fallen on the outer door frame?

Open hint 2

What does the thin mark near the chain’s fitting suggest?

Open hint 3

What do you have at hand to use as a tool you can operate from outside?

Solve It

Your question

How did the culprit set the door chain from outside?

Choose the answer closest to the truth.

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The Truth

He rigged a rubber band to pull the chain so that it would set by itself when the door was closed from outside

The answer is: he rigged a rubber band to pull the chain so that it would set by itself when the door was closed from outside.

Inside the room, the culprit placed the tip of the door chain near the entrance of the groove of the catch on the door frame, and used a rubber band to pull it in the closing direction. From outside, when he closed the door leaving a narrow gap, the force of the rubber band pulled the chain into the catch.

The rubber band that had fallen on the door frame and the thin mark on the chain’s fitting are the traces of that device.

The rubber band sets the chainInside, rig the chain tip to be pulled by a rubber bandFrom outside, close the door leaving a narrow gapThe rubber band pulls the chain into the catch, so it looks set from insideThe spent rubber band snaps and falls outside the frame
Diagram of the solution

Key Points

  • Small things at the scene (the rubber band) are traces of a tool
  • Ask whether the "inside" state could have been made from outside
  • "Good with his hands" is also a clue

Why people get fooled

You assume that "a chain is set from the inside," so you cannot think of a way to set it from outside.

Similar tricks

  • The locked room with a small tool
  • The type that doubts an assumption

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