The twenty-eight-year old Leon Czolgosz had been born into a large family of Polish immigrants in Detroit, and raised in Cleveland.  As a teenager, he was employed in various factories, but his family became increasingly concerned about his odd behavior.  Therefore, his father insisted that Leon only perform chores on the new family farm.  Young Czolgosz broke with the Catholic Church, and began reading anarchist and socialist literature.  In 1900, he became mesmerized by the assassination of King Humbert I of Italy by an anarchist, obsessively rereading accounts he had clipped from the newspaper.  The next year, Czolgosz attended anarchist meetings in Cleveland and Chicago, enthralled by the fiery orations of Emma Goldman.  The anarchists, though, feared that this strange young man was spying on them.

Czolgosz reached the conclusion that the assassination of President McKinley would send a warning to other national leaders, and generate positive publicity for the anarchist cause of overthrowing the political, economic, and religious establishment.  Czolgosz went to Buffalo in late August 1901 so that he could explore the grounds of the Pan-American Exposition, but apparently did not develop a specific plan for the assassination.  McKinley was protected at the event by three secret service agents, four additional guards, and several soldiers.  George Cortelyou, his personal secretary, and George Foster, chief of security, wanted to beef up security for the president, who had been receiving death threats, but McKinley dismissed their worries.

Czolgosz approached McKinley when the president's train arrived in Buffalo on September 4.  A policeman, thinking the assassin was an overzealous supporter, yelled at him to back off, and Czolgosz hurried away, afraid his intention would be discovered.  The next morning, he joined the crowd at the president's speech, and afterwards came near the presidential party as it was departing, but was unable to pick out McKinley from behind until it was too late to fire.  

On September 6, McKinley visited Niagara Falls, and then returned, against Cortelyou's wishes, to the Exposition's Temple of Music to shake hands with well-wishers.  Each person passed by a phalanx of guards to greet the president, but many entered with handkerchiefs in their hands, which they had used to wipe their brows in the hot sun outside.  Furthermore, the chief of security's place beside the president had been taken by an Exposition VIP. 

Czolgosz had wrapped a handkerchief around his hand and revolver, so that it resembled a bandaged hand.  The guards, distracted by another man they thought suspicious, let the assassin pass unmolested.  Czolgosz simply walked up and shot the president point blank in the chest (which ricocheted off a button) and a second time in the stomach.  The force of the bullets propelled McKinley backward onto the floor, while the soldiers fell on Czolgosz and unarmed him.  The president uttered, "Don't hurt him," and "My wife ... be careful how you tell her."

McKinley was transferred by ambulance to the Exposition hospital, and Czolgosz was taken to a local prison.  The physician on call, a gynecologist by training, performed the surgery, sewing up the entrance and exit wounds in the president's stomach, but was unable to locate the bullet.  Gangrene quickly set in, and Vice President Theodore Roosevelt, campaign manager Mark Hanna, and other colleagues and friends called at the president's bedside.  

On September 14, 1901, William McKinley became the third president in 36 years to die of an assassin's bullet.  Roosevelt, who had hurriedly returned to Buffalo the day before, was sworn in as the nation's youngest president (42).  After a state funeral in Washington, D.C., McKinley was buried in his hometown of Canton, Ohio, on September 19, as citizens across the country observed five minutes of silence at 3:30 in the afternoon.  His frail wife Ida never recovered from the loss, and died six years later.

At his trial, Czolgosz expressed no regrets and, while insisting he had no accomplice, declared his allegiance to Emma Goldman and anarchism.  After nine days, the jury returned a verdict of guilty, and Leon Czolgosz was executed by electric chair on October 29, 1901.