This was not entirely surprising to those who had watched the Louvre for years. The Mona Lisa was already, before the theft, an object that inspired unusually intense reactions from some visitors. But the nature of the reactions shifted. The painting had moved from an accessible artwork in an open gallery to a violated national possession — something France had lost. That framing changed everything about how the public thought about it.
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## The Investigation Begins
The initial investigation into the theft was handled by the French Sûreté, the national detective service, and by detectives assigned from the prefectural police. The scale of the response was significant for the era: by some accounts, sixty detectives were involved in the early stages of the investigation.
The investigators had little to work with. They had a physical evidence trail: the glass case and wooden frame found in the service stairway, and a single fingerprint left on the glass. They had the locked door that Peruggia had needed help to open, and the testimony of the plumber Sauvet. They had a rough timeframe — Monday, August 21, the closed maintenance day — and they had, eventually, a list of workers who had been inside the museum during that period.
The fingerprint was potentially valuable, but fingerprinting was still a relatively new forensic tool in 1911. French law enforcement was more familiar with the Bertillon system — a method of identifying individuals by body measurements — than with fingerprint matching as a primary investigative technique. The print was collected, documented, and compared against known records.