How to Play Capodoku: Murder Sudoku Rules

Capodoku is a murder mystery logic puzzle: you place every person from the case on the floor plan of a crime scene, and the floor plan tells you who did it. There are three rules, no luck and no trick questions. Read them once, then try today's Daily Case in your browser.

The goal: find the killer

Every case starts with a body. The floor plan of the scene is a square grid split into rooms by thick walls: a library, a dining car, a cabaret stage. Around the victim, a handful of suspects, each with one or two clues about where they stood.

Your job is to put every person, victim included, on exactly one square. Once the whole grid is filled in without breaking a rule, the killer reveals themselves. You never have to guess a motive. The geometry does the accusing.

Rule 1: one person per row and per column

A grid of 5 × 5 holds five people, a grid of 8 × 8 holds eight. Each row has exactly one person in it, and so does each column. This is the sudoku part of murder sudoku, and it does most of the work: every time you place someone, you remove a whole row and a whole column from everybody else's options.

Rule 2: every clue must be true

Clues are short, precise statements. A few examples, as they appear in the game:

"Frank is in the entrance hall." He is somewhere in that room.
"Dante is on a stool." He stands on one of the stools of the plan.
"Rosa is next to a plant." Her square shares a side with a square holding a plant, in the same room.
"Lola is in the leftmost column." No room is named, only the edge of the plan.
"Dante's row is higher than Sal's." Not necessarily directly above, just any row nearer the top.
"Sal is the only person in his room." Nobody else, victim included, may share it.

Negative clues ("Mario is not next to any table") count just as much as positive ones. When a clue mentions two people, it constrains both of them.

Rule 3: alone with the victim = killer

The killer is the only suspect in the same room as the victim. Once the victim is placed, look at their room: exactly one suspect will be in it. That person is the killer, and the case is closed.

This rule also works backwards while you solve. If two suspects are already confirmed in a room, the victim cannot be there. If a room has no possible suspect left, the victim is somewhere else.

Reading the crime scene (rooms, objects)

Walls. Thick dark lines separate rooms. A wall breaks contact: two squares on either side of a wall are never "next to" each other for a clue, even though they touch on the plan.

Next to. "Next to" means sharing a side, inside the same room. Corners do not count. Only one clue type uses corners, and it says so: "touches diagonally (corner to corner)".

Furniture you can stand on. Chairs, armchairs, rugs, stools, benches and beds hold a person. That is why "on a stool" makes sense.

Furniture that blocks. Pianos, bookshelves, plants, tables, stoves, cabinets, crates, counters, statues, bathtubs and desks fill their square. Nobody can stand there, but they still matter: they are what "next to a plant" or "next to a desk" refers to.

A good first look at any case: count the rooms, spot the rare furniture (a single piano narrows a clue a lot), and note which squares are blocked.

Worked mini-example (4×4)

Here is the practice case from our home page, The Aldo affair. Four people at the Manor: Gina, Sal, Rosa and Aldo, the victim. The plan has a living room (top left), a library (the whole right-hand column, plus the square beside it in the top row), a kitchen in the middle, and a conservatory along the bottom left. The clues:

Gina is sitting in an armchair.
Sal is standing next to the bookcase.
Rosa is next to the potted plant.
Aldo has no clue: his square will follow from everyone else's.

There is only one armchair, in the living room, row 2, column 1. Gina must be there, and row 2 and column 1 are now closed to everyone else.
Sal touches the bookcase, which stands in the library. The squares next to it, inside the library, are row 1, column 3 and row 2, column 4. Row 2 is taken by Gina, so Sal is in row 1, column 3.
Rosa touches the plant in the conservatory: row 3, column 2, row 4, column 1, or row 4, column 3. Columns 1 and 3 are already used, so Rosa is in row 3, column 2.
Only row 4 and column 4 are left: Aldo lies on the library rug, in the corner. Who else is in the library? Sal, and nobody else. Sal is the killer.

Four steps, no guessing. Bigger cases work exactly the same way, with more people and longer chains.

Difficulty levels

Every case carries one of four ranks.

Rookie. Direct clues do most of the work: rooms, edges, single pieces of furniture. Good for learning to read a plan.
Inspector. Clues start linking two people ("row is higher than", "same room as"), so you place people in pairs.
Chief. You need to see groups: two people who share the same two possible columns lock those columns for everyone else.
Legend. Some squares only fall to "what if" reasoning: suppose a suspect stands here, follow the consequences, and watch the case contradict itself.

In the app, grids go from 4 × 4 warm-ups up to 10 × 10. On this site, cases range from 5 × 5 to 8 × 8. Every single one, at every rank, has exactly one solution, checked by a solver before it is published.

If you know killer sudoku, the name can mislead: murder sudoku vs killer sudoku explains the difference. Unsure about a term? The glossary keeps them all in one place.

Next step: solving techniques

You now know everything the rules can tell you. The rest is method: where to start, which clues to combine first, and how to escape when you feel stuck. Our complete guide on how to solve murder sudoku walks through a full case. After that, the eight deduction techniques cover every situation the game throws at you.

When you want more than one case a day, the Capodoku app has full case files for iPhone, with the first one free.