Solution: The Empty Bottle at the Grand Hotel

The clues

• 
  PaulaThe opera singer between engagements.

  She was on an armchair.

• 
  AlmaThe retired botanist.

  She was beside a sofa.

• 
  ClaraThe young reporter.

  She was on a sofa.

• 
  WalterThe estate’s groundskeeper.

  He was in the fourth row.

• 
  Elena · VictimThe gallery owner.

  The victim. She was alone with the killer.

• 
  MateoThe waiter who hears everything.

  He was on a chair.

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. Pinned suspects Walter can only be in the fourth row, so nobody else can be there.
2. Room counting The victim, Elena, cannot be in the highlighted cells: her room there could not hold exactly one other person. The cells meant: row 1, column 1; row 1, column 2; row 2, column 1; row 2, column 2; row 2, column 6; row 3, column 1; row 3, column 2; row 3, column 4.
3. Shared rows and columns Alma and Clara can only be in the third row and the bottom row between them, so nobody else can be in those rows.
4. Pinned suspects Paula can only be in the second row, so nobody else can be there.
5. Pinned suspects Mateo can only be in the right column, so nobody else can be there.
6. Pinned suspects Alma can only be in the fourth column from the left, so nobody else can be there.
7. The only one who fits Only Elena can still reach the second column from the left, so she must be there. Placed: Elena: row 5, column 2 (Roof Terrace); Mateo: row 1, column 6 (Lounge).
8. The only one who fits Only Clara can still reach the third column from the left, so she must be there. Placed: Clara: row 3, column 3 (Kitchen); Alma: row 6, column 4 (Bar).
9. Room counting The victim, Elena, was on the Roof Terrace with exactly one other person. Only Walter can still get there. Placed: Walter: row 4, column 1 (Roof Terrace); Paula: row 2, column 5 (Lounge).