A GUIDE TO FAIR DEDUCTION
How to solve
murder mystery logic puzzles.
A good mystery grid doesn’t ask you to guess who looks guilty. It asks you to match the evidence until only one arrangement remains.
Murder mystery logic puzzles combine a fictional investigation with a set of rules. You may need to match each suspect to an object, a place, and sometimes an hour. The completed grid gives you the facts; the case’s question tells you which fact identifies the killer.
This guide explains the method used in One Fair Solution, a murder mystery puzzle book for adults. You can try its first case free online without an account. The small practice example below is separate from the book’s 40 cases and does not reveal the first case’s answer.
1. Start with the question and the known fact
Before marking the grid, read what the case asks you to identify. In One Fair Solution, the Known Fact explains how to recognize the killer, often by naming a particular object. You still need to work out who had that object and where they were.
Keep the story and the evidence in their proper roles. In this book, the numbered clues contain all the evidence needed to solve each case. Atmosphere, names, and illustrations are not secret clues.
2. Learn the one-to-one rule
Every person has exactly one value in each category, and no two people share a value. If Alex is at the front desk, neither Blake nor Casey can also be there. If Alex has the key, Alex cannot also have the lantern.
On a logic grid, mark a confirmed match with a dot and an impossible match with a cross. A blank square means “not decided yet,” rather than “no.” Once you confirm a match, cross out the other cells in that row and column of the same comparison grid.
3. Enter the direct clues first
Start with statements that give a fact immediately: “Alex was at the front desk” or “Blake did not have the key.” Record both positive and negative information. You do not need to solve the clues in their printed order.
Keep separate comparison grids straight. A mark in People & places does not automatically fill People & objects. Transfer a fact only when another clue or an established match connects the categories.
A SMALL, NON-MURDER PRACTICE EXAMPLE
Three people. Three objects. Three places.
Alex, Blake, and Casey each had one object: a key, a notebook, or a lantern. Each was in one place: the front desk, the boathouse, or the office. No two people shared an object or a place.
- Alex was at the front desk.
- The lantern was in the boathouse.
- Blake had the notebook.
- Casey had the lantern.
See the worked solution
Clues 2 and 4 put Casey in the boathouse: Casey has the lantern, and the lantern is there. Alex is at the front desk from Clue 1, so the remaining place, the office, belongs to Blake. Blake has the notebook from Clue 3. With the lantern and notebook assigned, Alex must have the key.
| Person | Object | Place |
|---|---|---|
| Alex | Key | Front desk |
| Blake | Notebook | Office |
| Casey | Lantern | Boathouse |
4. Transfer matches between categories
The useful move in the practice example is not a guess about Casey. It is a connection: Casey → lantern → boathouse. Once two confirmed facts share a value, you can connect the other values.
The same method works with exclusions. If an object cannot be in a certain place, the person confirmed to be at that place cannot have that object. Record the new cross in the correct comparison grid.
5. Eliminate possibilities, then revisit the clues
Look for a row or column with only one possibility left. Confirm that match, cross out its alternatives, and look again: a new mark can finish another row. Then reread clues that previously seemed unhelpful.
In harder puzzles, pay close attention to the exact wording. “Earlier” need not mean immediately before. Either-or statements and consecutive-hour clues can connect several facts. Use the puzzle’s stated rules rather than assumptions about how a crime usually happens.
If you need to test a remaining possibility, keep that assumption separate from confirmed facts. Check it against every relevant clue before treating it as proved.
6. Make a complete accusation
Return to the Known Fact and the original question. Write down the person, object, place, and hour if the case asks for one. A correct suspect name is only part of the answer when the puzzle also asks where and how.
If you get stuck, use a hint before reading the answer. One Fair Solution provides three progressive hints and a full walkthrough for each case, so you can check the deduction rather than simply copy the final name.