To understand the bombing, you have to understand the trial that preceded it. Thomas Mooney, a well-known labor militant and suspected dynamiter, had been convicted in 1916 for the Preparedness Day Bombing in San Francisco, which killed ten people and injured forty. But Mooney's trial was deeply suspect -- witnesses appeared coached, the atmosphere resembled a lynch mob more than a court of law. The case drew the attention of President Woodrow Wilson, who launched a letter-writing campaign urging Governor Stephens to commute Mooney's death sentence. In November 1917, just weeks before the mansion bombing, The San Francisco Call published an expose based on a federal investigation conducted under Wilson's orders, alleging that Mooney had been framed by prosecutors. The findings would prove prescient: the prosecution's case was later found to be riddled with perjury, corruption, suppression of evidence, and conflicts of interest.

When police arrived at the mansion, they found Stephens already wading through the wet, muddy basement, searching for clues about how the bomb had been placed. Neither the governor nor his guard had seen anything. Both believed the dynamite had been thrown from an alley about forty feet behind the house. Stephens declared the act to be terrorism, "the chief weapon of the alien enemy," a claim that dovetailed neatly with his recent series of public addresses urging support for the war effort. The timing mattered. America was ten months into World War I, and anti-immigrant, anti-radical sentiment was running at full boil. Blaming the IWW -- the Wobblies, as they were known -- required no evidence and met no skepticism, at least not initially.

On Christmas Eve, police arrested two IWW members after claiming they had picked up dynamite at the union's Sacramento headquarters. Three days later, the governor received an ultimatum letter demanding fifty thousand dollars or nine bombs across the city. Nothing came of the threat, but it gave authorities the pretext they needed. Police raided IWW locals across Northern California. In January 1918, fifty-one union workers were arrested and jailed, where five of them died -- four from the influenza epidemic sweeping the country and one from tuberculosis. Forty-six of the survivors were charged with conspiracy to violate the Espionage Act. Weeks after their trial, the California Criminal Syndicalism Act became law, making it a felony punishable by one to fourteen years in prison to advocate violence or sabotage as a means of political or industrial change. The statute was used for decades to silence political opponents until the Supreme Court struck it down nearly fifty years later.

As the anti-labor crackdown intensified, some began asking uncomfortable questions. The District Attorney's election had fallen the day after the bombing, and the wall-to-wall press coverage surely boosted his campaign. The bomber, whoever it was, had not seemed intent on killing anyone -- the explosion was dramatic but survivable. Sacramento's Chamber of Commerce and Downtown Association had been waging a months-long campaign against organized labor. Progressives grew suspicious. Then a San Francisco reporter working the story uncovered something darker: the mansion guard may have conspired with a prominent private detective named Martin Swanson to stage the entire attack. Swanson was no stranger to such tactics. He had previously attempted to frame Thomas Mooney in a similar scheme. Whether the bombing was a genuine act of radical violence or an elaborate provocation designed to justify a crackdown on labor remains unresolved. The question hangs over Sacramento's political history like smoke that never quite cleared.