Solution: The Visit After Midnight in the Gardens

The clues

• 
  OscarThe antiques dealer.

  He was in a corner of the room. He was in the left column.

• 
  ClaraThe young reporter.

  She was beside a chair.

• 
  FelixThe student who never sleeps.

  He was in the Coach House with another man.

• 
  GretaThe gardener who talks to her roses.

  She was not in a corner of the room.

• 
  MateoThe waiter who hears everything.

  He was in the top row.

• 
  Rafael · VictimThe bicycle courier.

  The victim. He was alone with the killer. He was in the Rose Garden with another man.

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 Mateo can only be in the top row, so nobody else can be there.
2. Pinned suspects Oscar can only be in the left column, so nobody else can be there.
3. Room counting The victim, Rafael, cannot be in the highlighted cells: his room there could not hold exactly one other person. The cells meant: row 2, column 6; row 3, column 6; row 4, column 6. Placed: Rafael: row 3, column 5 (Rose Garden); Oscar: row 6, column 1 (Coach House); Clara: row 4, column 4 (Greenhouse).
4. Pinned suspects Felix can only be in the fifth row, so nobody else can be there.
5. Room counting Rafael was in the Rose Garden with exactly one other man. Only Mateo can still get there. Placed: Mateo: row 1, column 6 (Rose Garden); Greta: row 2, column 2 (Maze); Felix: row 5, column 3 (Coach House).