The theft of the Mona Lisa has been called the “art heist of the century,” but the caper itself was fairly rudimentary. On the evening of Sunday, August 20, 1911, a small, mustachioed man entered the Louvre museum in Paris and made his way to the Salon Carré, where the Da Vinci painting was housed alongside several other masterworks. Security in the museum was lax, so the man found it easy to stow away inside a storage closet. He remained hidden there until the following morning when the Louvre was closed and foot traffic was light. At around 7:15 a.m., he emerged clad in a white apron—the same garment worn by the museum’s employees. After checking to see if the coast was clear, the thief strode up to the Mona Lisa, plucked it off the wall and carried it to a nearby service stairwell, where he removed its wooden canvas from a protective glass frame.

The lone hitch in the thief’s plan came when he tried to exit the stairwell into a courtyard. Finding the door locked, he placed the Mona Lisa—now wrapped in a white sheet—on the floor and tried to take apart the doorknob. He made little progress before one of the Louvre’s plumbers appeared on the stairwell. Rather than apprehending him, however, the plumber took the man for a trapped co-worker and assisted him in opening the door. With a friendly thank you, the thief made his getaway. Just a few moments later, he waltzed out of the Louvre with one of the world’s most valuable paintings tucked beneath his apron.

For more than a day, the Louvre’s staff had no clue that the Mona Lisa had been stolen. The museum’s paintings were often removed from the walls for cleaning or photography, so passersby took little notice of the blank space where the portrait was usually located. Finally, at around noon on Tuesday, a visiting artist asked a security guard to track the painting down. When the guard couldn’t locate it, the museum called the police and began a frantic search. It was only then that the Mona Lisa’s glass frame was discovered in the service stairwell. That same evening, a museum official announced the theft to the world. “The Mona Lisa is gone,” he said. “Thus far we haven’t a clue as to who might have committed this crime.”

News of the disappearance prompted a public outcry in France. “What audacious criminal, what mystifier, what maniac collector, what insane lover, has committed this abduction?” wondered the Parisian magazine L’Illustration. An army of detectives descended on the Louvre to dust for fingerprints and question witnesses. Cars, steamer passengers and pedestrians were searched at checkpoints, and police circulated “wanted posters” of the Mona Lisa’s enigmatic half-smile. When the Louvre finally reopened a week later, thousands of people came to gawk at the empty wall where the painting had once hung.

Despite the media circus, the police investigation turned up few promising leads. One high-profile suspect was Guillaume Apollinaire, an avant-garde poet who had once called for the Louvre to be burned down. Apollinaire was arrested in September 1911 after police linked him to the earlier theft of two ancient statuettes, which had been lifted from the Louvre by his secretary. During his interrogation, he implicated his close friend Pablo Picasso, a 29-year-old Spanish artist who had purchased the statuettes and used them as models in his paintings. While the authorities questioned Apollinaire and Picasso in connection with the Mona Lisa’s disappearance, the two future art legends were later cleared due to lack of evidence.

As days turned into months, speculation on the Mona Lisa’s whereabouts ran rampant. The New York Times wrote that “a great number of citizens have turned amateur Sherlock Holmeses, and continue to advance most extraordinary theories.” Some argued that American banking magnate J.P. Morgan had commissioned the heist to bolster his private art collection; still others believed the Germans had masterminded it to disgrace the French. Alleged sightings filtered in from such far-off locales as Brazil, Russia and Japan, but more than two years eventually passed without a break in the case. Many began to believe that Da Vinci’s 400-year-old masterpiece was lost for good.

Unbeknownst to police, however, the Mona Lisa was still in France. In fact, from the very day that it was stolen, it had languished in a one-room apartment on the outskirts of Paris. Its thief was Vincenzo Peruggia, an Italian immigrant who had once worked at the Louvre as a handyman. He had even helped construct the Mona Lisa’s protective frame. After making off with the painting in August 1911, the 29-year-old had stashed it in his home in a wood trunk with a false bottom. As a former Louvre employee, he was questioned about the theft on two separate occasions, but police never considered him a serious suspect. Peruggia kept the Mona Lisa hidden for two years while he waited for the heat to die down. “I fell a victim to her smile and feasted my eyes on my treasure every evening,” he later said. “I fell in love with her.”

Peruggia finally made an attempt to sell his “treasure” in December 1913. Using the alias “Leonard,” he sent a letter to a Florentine art dealer named Alfredo Geri and informed him that he had stolen the Mona Lisa and wanted to repatriate it to Italy. After conferring with Giovanni Poggi, director of Uffizi Gallery, Geri invited Peruggia to Florence and agreed to take a look at the painting. A few days later, the three men gathered in Peruggia’s hotel room, where he produced a mysterious object wrapped in red silk. “We placed it on the bed,” Geri later wrote, “and to our astonished eyes the divine Mona Lisa appeared, intact and marvelously preserved.” The Florentines immediately arranged for the painting to be taken to the Uffizi. They also agreed to Peruggia’s 500,000-lire sales price, but they had no intention of actually buying the Mona Lisa. Instead, after having the portrait authenticated, they reported the thief to the authorities. On the afternoon of December 11, 1913, police arrested Peruggia at his hotel.

Getty Images / Roger Viollet
Authorities inspecting the recovered Mona Lisa in Florence.

After a brief tour through Da Vinci’s homeland, the Mona Lisa was finally returned to the Louvre in January 1914. Peruggia, meanwhile, was charged with theft and put on trial in Italy. During his testimony, he claimed that national pride had inspired him to steal the painting, which he believed had been looted from his native Italy during the Napoleonic era. Peruggia was mistaken—Da Vinci had brought the Mona Lisa to France in 1516, and King Francois I had later purchased it legally—but the patriotic defense won him legions of admirers. Even after the prosecution presented evidence that he planned to shop the painting around to art dealers and sell it for profit, many Italians still considered him a national hero. In the end, he was sentenced to one year and 15 days in prison but served just seven months before winning his release on appeal. He later fought in the Italian army during World War I before returning to France, where he died in 1925.

While Peruggia was eventually forgotten, his daring heist only made the Mona Lisa more famous. At least 120,000 people went to see the painting in the first two days after it was returned to the Louvre. Art lovers and critics launched into fresh speculation about its subject’s mysterious smile, and it was referenced in countless cartoons, advertisements, parodies, postcards and songs. “The Mona Lisa had left the Louvre a work of art,” author Dianne Hales later wrote. “She returned as public property, the first mass art icon.” Today, the world’s most recognizable painting remains in the Louvre, where it hangs in a climate-controlled box protected by bulletproof glass. It receives some 8 million visitors each year.