Solution: The Lie at the Premiere at the Theatre

The clues

• 
  TheoThe paperboy.

  He was on a sofa.

• 
  QuentinThe butler of forty years.

  He was in the Corridor with another man. He was in the right column.

• 
  KarimThe family lawyer.

• 
  ZoeThe tattoo artist.

  She was not in a corner of the room.

• 
  Hugo · VictimThe retired colonel.

  The victim. He was alone with the killer. He was in the Cloakroom.

• 
  ElenaThe gallery owner.

  She was on a rug. She was in the top row.

Step by step

The order our solver finds. Each step uses only the clues and what the steps before it proved, and its heading links to the technique.

1. Last cell left Every other cell is ruled out for Elena, by her testimony or by a row or column already taken. Placed: Elena: row 1, column 1 (Cloakroom).
2. Pinned suspects Quentin can only be in the right column, so nobody else can be there.
3. Room counting The victim, Hugo, was in the Cloakroom with exactly one other person, who is already there. Nobody else can be in that room. Placed: Theo: row 3, column 5 (Box Office).
4. Pinned suspects Hugo can only be in the third column from the left, so nobody else can be there.
5. Room counting Quentin was in the Corridor with exactly one other man. Only Karim can still get there. Placed: Karim: row 6, column 4 (Corridor); Zoe: row 5, column 2 (Dressing Room); Quentin: row 4, column 6 (Corridor); Hugo: row 2, column 3 (Cloakroom).