A wet black umbrella was found folded in the corner of the studio. There was no rain that night — the umbrella could only be wet from canal water. The killer entered through the private boat landing at the rear.
An unsigned letter reading "You will regret dismissing me" was found in the desk drawer. Forensics matched the ink to a pen belonging to art dealer Luca Bianchi.
A ledger hidden behind a rolled canvas recorded the sale of 6 forged paintings at high prices. The initials "S.M." are listed as the forger — initials matching one of the suspects the professor knew closely — with a scheduled handover of information to "the authorities" on Thursday.
The front dock's camera log shows Luca arrived at 6:00 PM and departed at 7:45 PM — over an hour before the time of death. The private rear mooring has no camera coverage.
Sofia Martin is the killer.
The secret ledger reveals that Professor Ferrara was about to report to the authorities on Thursday that "S.M." — Sofia Martin — had painted all 6 forgeries. Sofia knew this and had to silence him.
She claimed to have left by public vaporetto at 8:30 PM, but Marco confirmed the last vaporetto departed at 8:45 PM — meaning she could have returned via the studio's private kayak at the camera-free rear mooring. The wet umbrella inside the studio proves someone arrived damp from canal water on a rainless night — this is the piece of evidence that most directly identifies the killer.
Luca's threatening letter and apparent motive were a red herring — the dock log and reception witnesses conclusively place him off the island before the time of death. Sofia's claim that she "did not return to the studio that night" was a lie.
Marco Rizzi is not a suspect — he had no connection to the forgeries, no motive whatsoever, and served as a reliable witness throughout the investigation.