The murder of Louis Cadiou in the town of Landerneau, located in the Finistère department of France, remains a subject of fascination nearly a century after the fact. Cadiou was an industrialist, a man whose life and work were deeply tied to the region's economy. His death occurred during World War I, a time of global conflict and political tension that shaped many events across Europe. The circumstances surrounding his murder have raised many questions, particularly due to the way the investigation was handled. Cadiou was found dead in his home in 1915, and the case quickly became a local scandal. The police investigation was criticized for being poorly conducted, with many believing that key evidence was overlooked or mishandled. This lack of thoroughness led to the swift arrest of a suspect, who was charged with the crime. However, the trial that followed was inconclusive, and the accused was ultimately acquitted. This outcome only deepened the mystery, as no one was ever officially identified as the killer. The case took on an even more complex dimension due to the political climate of the time. World War I had already begun, and suspicions of espionage and sabotage were widespread. Some have speculated that Cadiou's murder might have been linked to these fears, though no conclusive proof has ever emerged. The lack of a clear resolution has led to ongoing speculation and theories about what really happened that night. While the Seznec affair is often cited as one of the most famous unsolved mysteries of the early 20th century, the story of Louis Cadiou's murder is equally compelling. It reflects the broader uncertainties and tensions of the period, as well as the challenges of justice during wartime. Despite the passage of time, the case continues to intrigue historians, local residents, and those interested in the unsolved mysteries of the past.