Whodunit

How to play Whodunit

Whodunit is a logic grid puzzle dressed as a murder mystery. Each case has a handful of suspects, weapons and rooms — and on hard cases, motives — and every suspect had exactly one of each. Nobody shared anything. The clues pin down who had what and who was where, and one more fact, where the body was found, turns all of that into an answer: who did it, with what, and where.

Logic grid puzzles have filled the back pages of puzzle magazines for decades, and the murder-mystery version has become a favourite in recent years. Every case here has exactly one answer, and it can always be reached by reasoning, without guessing.

The grid

The grid compares every category with every other one, in blocks: suspects against weapons, suspects against rooms, rooms against weapons, and so on. Each small square asks one question — did these two go together?

• Tap once for a cross: these two cannot go together.
• Tap twice for a tick: these two go together.
• Tap a third time to clear the square.
• With cross out automatically on (the default), a tick crosses out the rest of its row and column in that block, since each suspect has only one of each thing. Clear the tick and those crosses go with it, unless another tick still rules the square out. Crosses you put in yourself always stay.

Reading the clues

• "Colonel Brandt was not in the attic" — a cross, straight away.
• "The person with the rope was not in the kitchen" — a cross between the rope and the kitchen. Whoever turns out to have the rope was not in the kitchen either, so it carries over to the suspects once you know who had it.
• "Miss Fenwick had either the wrench or the brick" — every other weapon is crossed out for her. Once one of those two is ruled out, she had the other.
• Tap a clue to cross it off the list once you have used it, so you can see what is left to read.

How to solve it

Most cases fall to the same few ideas, used over and over.

• One left is the answer. When a row in a block has only one square not crossed out, that square is a tick.
• Ticks travel. If Lady Ashworth had the rope and the rope was in the library, Lady Ashworth was in the library. Copy every tick across to the other blocks.
• Crosses travel with ticks. If Lady Ashworth had the rope, and the rope was not in the cellar, Lady Ashworth was not in the cellar either.
• No common ground, no match. If two things have no possible partner in common in a third category, they cannot go together.

Making your accusation

When you know the answer, choose who, with what and where — and why, on a hard case — and press Accuse. A wrong accusation does not end the case, but it is counted, and it shows on your result. You do not have to finish the whole grid first: once the clues point clearly at the person in the murder room, you can accuse.

Hint puts one square right: a wrong mark if you have one, otherwise the next square the clues decide, with the fact it stands for written out. Hints are counted too.

Case sizes and the daily

Easy cases have three suspects, weapons and rooms; medium cases have four. Hard cases have four of each and add a motive for every suspect, which brings three more blocks to the grid.

The daily case is the same for everyone and follows the week: easy on Monday and Tuesday, medium from Wednesday to Friday, and hard at the weekend. Closing it keeps your streak going, and the result can be shared without giving the answer away.

How the cases are made

Each case is built in your browser around a hidden answer. First the suspects are dealt their weapons and rooms at random; then every true clue about that answer is written out — who had what, what did not go together, and either-or clues that pair the truth with a decoy.

Then clues are taken away one at a time, plain "X had the Y" clues first — they give an answer away, so they are almost always the ones that go. After each removal a solver tries to finish the grid using only the reasoning described above. If it still can, the clue stays out; if not, it goes back. What is left is a short list of clues that still leads to exactly one answer, by reasoning alone.

Common questions

Do I ever need to guess?

No. Every case is checked by a solver that only uses reasoning, so the clues always lead to the answer without trial and error.

What happens if I accuse the wrong person?

Nothing dramatic: the case stays open and the wrong accusation is counted. Your result shows how many you made.

Is this like Murdle?

It is the same kind of puzzle — a logic grid with a murder mystery story — written and generated for this site. Like other daily puzzles here, there is a new case every day, free.

Why are the grid headers pictures?

So the grid fits on a phone. Names do not fit across a narrow screen, so each suspect, weapon and room has its own picture, and the key above the grid says which is which.