The accusations were explosive: a head of state had not only begun an illegal war, but egged his troops on to a series of horrific atrocities that left thousands dead and an entire continent in ruins. By then, the accused was one of history’s most hated and debated figures, a monarch known for making erratic decisions and doubling down on his sometimes inexplicable actions.

There was just one problem: The accused, Wilhelm II of Germany, couldn’t testify. The accused had been dead for 75 years.

It could have been the trial of the century—if it had been conducted a century before. The trial of Wilhelm II, Germany’s emperor between 1888 and 1918, was a moot one, conducted by historians and legal experts grappling with one of the great mysteries of 20th-century history. Was Wilhelm II guilty of war crimes?

It’s a question that was never answered during Wilhelm’s lifetime. Though the Allies accused him of starting one of history’s bloodiest wars and violating international law, and his troops of committing barbaric acts, he never stood trial. Today, these accusations are remembered as the first stirrings of a modern conception of war crimes. But at the end of World War I, Wilhelm’s responsibility for the bloodshed was a hotly contested—and ultimately unresolved—issue.

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Wilhelm was never tried, and died in exile in 1941. Historians are still split on his role in causing World War I. So how did the deposed Kaiser fare in his posthumous “trial”? The verdict was mixed. Though the historians found him guilty of causing German troops to invade neutral Belgium, they acquitted him on all other counts.