How to solve a murder mystery logic puzzle
A good murder mystery logic puzzle gives you everything you need and nothing you can take on trust. These techniques are written for Whodunnit's rules, but most of them work on any whodunnit puzzle with liars.
1. Sort what you can trust from what you can't
In Whodunnit, a suspect can only lie about one thing: where they were themselves. So:
- “Where were you?” might be a lie.
- “Who was with you?” is always true about the people it names, even from a Liar.
- “What's your sister like?” is always true.
Build your case on the answers that can't be lies, and treat every “I was in the Kitchen” as a claim to check.
2. Use the people, not the rooms
When someone says “Ben was with me”, Ben really was in that room. If Ben later claims a different room, Ben is lying. If someone else claims that room and wasn't on the list, they're lying. One “Who was with you?” can confirm or sink several stories at once.
3. Nobody claims the crime scene
The culprit is never Honest, and a Liar never names the crime scene. So nobody will ever tell you they were there. The case is about who is missing from the other rooms.
4. Count the liars
The case file tells you how many Liars and Evasive suspects there are. Once you've caught that many, everyone else is Honest, and their room is simply true.
5. Place everyone else
Exactly one person was at the scene. Every suspect you can place somewhere else is cleared. When only one is left unplaced, you have your culprit, whether or not you ever caught them in a lie.
6. A refusal is not a confession
An Evasive suspect won't say where they were, but an innocent one can be Evasive too. Place them through other people's answers before you charge them.
A worked example
The crime happened in the Study. The other rooms are the Kitchen and the Garden. Three suspects: Ada, Ben and Cora. The case file says there is 1 Liar and nobody Evasive.
| # | Question | Answer |
|---|---|---|
| 1 | Ada, where were you? | “The Kitchen.” |
| 2 | Ada, who was with you? | “Ben.” |
| 3 | Cora, where were you? | “The Garden.” |
| 4 | Cora, who was with you? | “Nobody.” |
| 5 | Ben, where were you? | “The Kitchen.” |
| 6 | Ben, who was with you? | “Ada.” |
After question 2, Ben is cleared. Ada's list is true, so Ben really was in the Kitchen.
After question 4, both stories still fit. Either Ada is the Liar and was in the Study, or Cora is the Liar and was in the Study. Cora's “Nobody” is true either way, so nobody else was in the Garden, but that doesn't place Cora herself.
After question 6, it's solved. Ben's list is true, so Ada really was in the Kitchen. She's cleared, and she's Honest. The only suspect left is Cora. She was in the Study and lied about the Garden. Charge her.
Could it be done faster? Yes: questions 1, 2, 5 and 6 are enough. Ada and Ben place each other in the Kitchen, and Cora is the only one left, without asking her anything. Finding that shorter route is what par is about.
Try it on today's case
Every Whodunnit case has exactly one answer, and asking everyone where they were and who was with them always fits in your 10 questions. Start there, and cut questions as you learn the shortcuts.
Play today's case, #3