Borrowing $15 from a Mr. Maynard, Guiteau went out to purchase a revolver. He knew little about firearms, but did know that he would need a large caliber gun. He had to choose between a .442 Webley caliber British Bulldog revolver with wooden grips or one with ivory grips. He chose the one with the ivory handle because he wanted it to look good as a museum exhibit after the assassination. Though he could not afford the extra dollar, the store owner dropped the price for him. (The revolver was recovered, and even photographed by the Smithsonian in the early 20th Century, but it has since been lost.) He spent the next few weeks in target practice—the kick from the revolver almost knocked him over the first time—and stalking Garfield.
On one occasion, he trailed Garfield to the railway station as the President was seeing his wife off to a beach resort in Long Branch, New Jersey, but he decided to shoot him later, as Garfield's wife, Lucretia, was in poor health and Guiteau did not want to upset her. On July 2, 1881, he lay in wait for Garfield at the (since demolished) Baltimore and Potomac Railroad Station, getting his shoes shined, pacing, and engaging a cab to take him to the jail later. As Garfield entered the station, looking forward to a vacation with his wife in Long Branch, Guiteau stepped forward and shot Garfield twice from behind, the second shot piercing the first lumbar vertebra but missing the spinal cord. As he surrendered to authorities, Guiteau said: "I am a Stalwart of the Stalwarts. .. Arthur is president now!'"
After a long, painful battle with infections, possibly brought on by his doctors' poking and probing the wound with unwashed hands and non-sterilized instruments, Garfield died on September 19, eleven weeks after being shot. Most modern physicians familiar with the case state that Garfield would have easily recovered from his wounds with sterile medical care, which was common in the United States ten years later. While Candice Millard argues that Garfield would have survived Guiteau's bullet wound had his doctors simply left him alone, Garfield's biographer Peskin stated that medical malpractice did not contribute to Garfield's death; the inevitable infection and blood poisoning that would ensue from a deep bullet wound resulted in multiple organ damage and spinal bone fragmentation.
Trial and execution
Once Garfield died, the government officially charged Guiteau with murder. He was formally indicted on October 14, 1881, for the charge of murder, which was previously attempted murder after his arrest. Guiteau pleaded not guilty to the charge. The trial began on November 14, 1881, in Washington, D.C. The presiding judge in the case was Walter Smith Cox. Guiteau's court-appointed defense lawyers were Leigh Robinson and George Scoville, although Guiteau would insist on trying to represent himself during the entire trial. Wayne MacVeagh, the U.S. Attorney, served as the chief prosecutor. MacVeagh named five lawyers to the prosecution team: George Corkhill, Walter Davidge, John K. Porter, Elihu Root, and E.B. Smith.
Guiteau's trial was one of the first high-profile cases in the United States where the insanity defense was considered. Guiteau vehemently insisted that while he had been legally insane at the time of the shooting, he was not really medically insane, which was one of the major causes of the rift between him and his defense lawyers.
Dr. Edward Charles Spitzka, a leading alienist, testified as an expert witness. Dr. Spitzka had stated that it was clear "Guiteau is not only now insane, but that he was never anything else." While on the stand, Spitzka testified that he had "no doubt" that Guiteau was both insane and "a moral monstrosity." Spitzka came to the conclusion that Guiteau had "the insane manner" he had so often observed in asylums, adding that Guiteau was a "morbid egotist" who "misinterpreted and overly personalized the real events of life." He thought the condition to be the result of "a congenital malformation of the brain."
George Corkhill, who was the District of Columbia's district attorney and on the prosecuting team, summed up the prosecution's opinion of Guiteau's insanity defense in a pre-trial press statement that also mirrored public opinion on the issue. Corkhill stated the following:
He's no more insane than I am. There's nothing of the mad about Guiteau: he's a cool, calculating blackguard, a polished ruffian, who has gradually prepared himself to pose in this way before the world. He was a deadbeat, pure and simple. Finally, he got tired of the monotony of deadbeating. He wanted excitement of some other kind and notoriety, and he got it. — George Corkhill – District attorney for District of Columbia
Guiteau became something of a media sensation during his entire trial for his bizarre behavior, which included him frequently cursing and insulting the judge, most of the witnesses, the prosecution, and even his defense team, as well as formatting his testimony in epic poems which he recited at length, and soliciting legal advice from random spectators in the audience via passed notes. He dictated an autobiography to the New York Herald, ending it with a personal ad for "a nice Christian lady under 30 years of age". He was oblivious to the American public's hatred of him, even after he was almost assassinated twice himself. He frequently smiled and waved at spectators and reporters in and out of the courtroom, seemingly happy to be the center of attention for once in his life. Guiteau attempted to convince President Chester A. Arthur to set him free through a letter as he had just increased Arthur's salary by making him president. At one point, Guiteau argued before Judge Cox that President Garfield was killed not by the bullets but by medical malpractice ("The doctors killed Garfield, I just shot him"), which, if one discounts the fact that Guiteau had been responsible for Garfield needing that medical attention in the first place, was more than a little true. Guiteau's argument had no legal support, however. Throughout the trial and up until his execution, Guiteau was housed at St. Elizabeths Hospital in the southeastern quadrant of Washington, D.C. While in prison and awaiting execution, Guiteau wrote a defense of the assassination he had committed and an account of his own trial, which was published as The Truth and the Removal.
To the end, Guiteau was actively making plans to start a lecture tour after his perceived imminent release and to run for president himself in 1884, while at the same time continuing to delight in the media circus surrounding his trial. He was found guilty on January 25, 1882. After the guilty verdict was read, Guiteau stepped forward, despite his lawyers' efforts to tell him to be quiet, and yelled at the jury saying "You are all low, consummate jackasses!" plus a further stream of curses and obscenities before he was taken away by guards to his cell to await execution. Guiteau appealed his conviction, but his appeal was rejected, and he was hanged on June 30, 1882, in the District of Columbia, just two days before the first anniversary of the shooting. Of the four presidential assassins, Guiteau lived longer than any after his victim's death (nine months). While being led to his execution, Guiteau was said to have continued to smile and wave at spectators and reporters, happy to be at the center of attention to the very end. He notoriously danced his way to the gallows and on the scaffold as a last request, he recited a poem he had written during his incarceration which he called "I am Going to the Lordy." He had originally requested an orchestra to play as he sang his poem, but this request was denied.
Part of Guiteau's brain remains on display at the Mütter Museum in Philadelphia and National Museum of Health and Medicine in Maryland