How to solve logic grid puzzles: a detective's guide
Updated 25 October 2026 · about 6 minutes to read
A logic grid puzzle (also called a zebra puzzle or Einstein's riddle) gives you a few lists of things and a set of clues. Each item in one list pairs with exactly one item in every other list, and the clues are enough to work out every pairing without guessing. Murder mystery puzzles like Whodunnit use the same idea: the lists are suspects, rooms and weapons, and the last pairing you find tells you who did it.
This guide walks through the methods that solve almost every grid, with a small worked case you can follow on paper.
1. Set up the grid
Draw one small table for every pair of lists: suspects against rooms, suspects against items, and rooms against items. Each square answers one question, such as "was the Cook in the Library?" You will fill it with one of two marks:
- ✗ means "no, these two don't go together".
- ✓ means "yes, these two go together".
In Whodunnit the detective notebook is this grid, already drawn for you.
2. A ✓ crosses out its whole row and column
This is the rule that does most of the work. Because each suspect was in exactly one room, and each room held exactly one suspect, a ✓ means every other square in the same row and the same column is ✗. Always fill those in straight away. (The Whodunnit notebook does this for you when you place a ✓.)
3. The last empty square must be ✓
The reverse is just as useful. If a row has a ✗ in every square but one, the last square must be a ✓. Scan your rows and columns for this after every few marks; it is how most "stuck" moments end.
4. Carry facts across grids
Once you know two things go together, they share everything. If the Maid was in the Garden, and whoever was in the Garden had the rope, then the Maid had the rope. Copy facts from one grid into the others as soon as you find them, and copy ✗ marks too: if the Maid was in the Garden and the Garden did not hold the knife, the Maid did not have the knife.
5. Read every clue for what it rules out
Most clues are negative ("the Butler was not in the Kitchen"), and each one is a single ✗. Some clues hide two facts: "the person with the candlestick was not the Cook and was not in the Garden" gives you two ✗ marks in two different grids. Clues that link two non-people ("the rope was in the Garden") belong in the rooms-against-items grid.
A worked case
The suspects: the Cook, the Butler and the Maid. The rooms: Library, Kitchen, Garden. The items: rope, candlestick, knife. The body was found in the Library.
- The Cook was in the Kitchen.
- The Maid was not in the Library.
- Whoever had the rope was in the Garden.
- The Cook did not have the knife.
Clue 1 is a ✓: Cook–Kitchen. Cross out the rest of that row and column, so the Cook was not in the Library or Garden, and nobody else was in the Kitchen.
Clue 2 is a ✗: Maid–Library. The Maid's row now has one empty square left, the Garden, so the Maid was in the Garden (rule 3). That leaves the Butler with the Library.
| Library | Kitchen | Garden | |
|---|---|---|---|
| Cook | ✗ | ✓ | ✗ |
| Butler | ✓ | ✗ | ✗ |
| Maid | ✗ | ✗ | ✓ |
Clue 3 links an item to a room: rope–Garden. Carry it across (rule 4): the Maid was in the Garden, so the Maid had the rope.
Clue 4: the Cook did not have the knife, and the rope is taken, so the Cook had the candlestick. The Butler had the knife.
The body was in the Library and the Butler was the one in the Library. The Butler did it, with the knife. Notice that no step needed a guess: every mark came from a clue or from rules 2 to 4.
6. Harder cases: times, leads and liars
- A fourth list. Some cases add the time each suspect was seen. Nothing changes except that there are more grids; the same rules apply to every pair.
- Leads. In some Whodunnit cases you start with only part of the clues and choose when to follow a lead for another. Before following one, squeeze everything you can from what you have; the Inspector's par is the fewest leads that make the case solvable.
- "The murderer always lies." When suspects make statements and only the murderer lies, try each suspect in turn: assume they are the liar, treat their statements as false and everyone else's as true, and see whether the clues still fit. Every assumption except one ends in a contradiction (two ✓ marks in one row, for example). The one that survives names the murderer.
7. When you're stuck
- Re-read each clue and ask "what does this rule out?" rather than "what does this prove?"
- Check every row and column for a single empty square.
- Look for facts you found in one grid but haven't copied into the others.
- As a last resort, try a mark in pencil and follow it until it breaks. If it breaks, the opposite is true. Good puzzles never need this, but it is a fair way to learn.
Practise on a real case
Whodunnit is a free murder mystery logic game in your browser. Every case has exactly one answer you can prove from the clues, the first case walks you through the notebook step by step, and a new daily case arrives every day.
More guides: How to play · How to solve logic grid puzzles · Games like Murdle · Privacy