On the afternoon of May 4th, a passerby on Brunswick Street, a bohemian strip in northeast Melbourne, Australia, noticed another man tagging shop fronts with graffiti stickers. Displeased, he asked the man to stop and then, when the man continued, began filming his actions with a mobile phone. This led to an argument and a tussle. When the passerby got the tagger in a headlock, he accidentally butt-dialled his sister. She heard sounds of a struggle on the other end of the line and called the police.

The police arrested the vandal, a pale, lanky American named Jim Clay Harper. As it turned out, Harper had been on the lam since 2011, having left the United States in violation of probation for graffiti-related crimes. Harper and Danielle Bremner, his partner in graffiti and love, who wasn’t with Harper at the time of the arrest, specialized in defacing trains. They had spent the past six years travelling and spray-painting the world’s public-transit systems, like surfers chasing the next big wave.

Harper had been doing graffiti since he was a student at Bowling Green State University, in Ohio. Raised in the affluent Chicago suburb of Wilmette, Harper met Bremner, who is a few years older, in 2005, through a mutual friend. Bremner, nymph-like, with big eyes and a ski-jump nose, had previously lived in New York, but had moved to Chicago the year before. They were both already established in the graffiti scene, and the plan was to meet in Chicago and make a quick trip to St. Louis to paint the city’s light-rail system. Their friendship was instant. Pretty soon, Harper was leaving campus regularly to connect with Bremner for train-painting excursions across the U.S, driving from one town to the next, sleeping in Bremner’s car, and painting trains with his tag, ETHER, and hers, UTAH and DANI.

They worked as part of a crew of about thirty graffiti vandals called Made U Look, or MUL, most of whom were based in Chicago. To prepare for their “actions,” as they called them, Harper and Bremner would use Google Earth and other satellite imagery to research train yards and the various points of access. They’d stake out locations for days, sometimes finding surveillance cameras and looking for their blind spots. Once on site, they’d sometimes wear reflective vests, a standard uniform for train workers, to blend in. More than once, a worker mopped the floor inside the train as Harper, Bremner, and other crew members painted the outside.

They were among a small subset of graffiti artists—a subculture within a subculture—emerging in the early two-thousands who were bent on reviving large-scale actions focussed exclusively on public transit. Unlike the graffitists of the nineteen-seventies and eighties, whose elaborate works were the wallpaper of New York City subways, these writers knew their work was ephemeral and would be scrubbed off before it ever left the train yard. But mobile-phone cameras allowed a new sort of notoriety. The goal was to document their daring acts and then post the images on the Internet.

Every few months, Harper and Bremner released flicks—images, which would appear on graffiti forums, Web sites, and online magazines—as proof of their conquests. “High quality, mass quantity” was Harper’s motto. As he and Bremner kept painting, they often added a degree of difficulty by painting cartoon characters—the Tasmanian Devil, Marvin the Martian, and SpongeBob SquarePants—and text to accompany their train “panels.” This was a MUL signature and a boast to rival graffiti writers. MUL’s efforts reached a pinnacle in 2006, when, on Christmas Eve, half a dozen crew members painted ten New York City subway cars with a Monopoly motif. It was a feat that required the skill and organization of a bank heist—fifteen gallons of paint and ninety cans of spray paint, and hours spent under the city’s busy streets, covering nearly a thousand feet of train in white, green, and black paint, and finishing the job off with a large-scale rendering of Rich Uncle Pennybags, the game’s deep-pocketed mascot.

Not long after the Monopoly train incident, Detectives Anthony Navarra and Jonathan Dubroff, of the Citywide Vandals Task Force of the New York City Police Department’s Transit Division, started investigating Harper and Bremner. “They were doing pretty expensive damage to New York City subway trains,” Navarra recalled. Somewhere between a hundred thousand and two hundred thousand dollars in total, according to reports. Riders on New York City subway trains don’t see much graffiti anymore. Improvements, like new train cars and a policy of quickly buffing off graffiti before the trains went into service for the day, effectively put an end to the public display of the practice after years of failed efforts (including barbed-wire-topped fences guarded by a small army of German shepherds). On May 12, 1989, the New York City Transit Authority officially declared that the city’s subways were graffiti-free.

Graffiti didn’t disappear, of course; it just moved from trains to buildings. And the revival of a subculture of train-graffiti writing in the years after the 2001 terrorist attacks on the World Trade Center was seen as more than an irksome act of vandalism. Breaking into a transportation hub was more challenging than it had been before terrorism was a real threat, and was viewed by the authorities as a major breach of security.

Over many months, Navarra and Dubroff subpoenaed Harper and Bremner’s phone records and e-mail accounts, followed them in surveillance vehicles, and executed a search warrant on Bremner’s apartment, in Queens, where they found two hundred cans of spray paint. In early August of 2008, a grand jury indicted Bremner and Harper on crimes including felony criminal mischief and burglary. By the time the indictments came down, however, the couple had left the country. They were in Europe, on a four-month graffiti spree. It was only on August 19, 2008, when they returned to the United States, that the authorities caught them. Navarra was on hand at John F. Kennedy Airport to arrest Harper. Navarra was so thrilled finally to have caught his most elusive vandal that he asked to take a picture with Harper, who agreed.

After their arrests, the media dubbed Harper and Bremner the Bonnie and Clyde of graffiti, and described how they “traipsed” across Europe, defacing subway trains as they went. Gawker called Bremner “the new hipster folk hero,” and the New York Post cited them as “two of New York’s most notorious graffiti vandals.” They were each sentenced to six months in jail in New York and another six months in Boston, where they had also been convicted of painting subway trains, and were required to complete five years of probation.

I met Harper in the spring of 2010, when he was serving his six-month sentence for train graffiti on Rikers Island. Bremner had recently completed her sentences, so she accompanied me to the jail. She told me she’d spent much of her time while incarcerated sleeping. Harper, though, had been passing his jail term drawing, selling commissioned pictures to other inmates for a few bucks apiece. He also worked in the kitchen. The rapper Lil Wayne had arrived a few months earlier, and as part of Harper’s job he sometimes delivered meals to Wayne in his protective-custody cell. Harper was polite and soft-spoken, apologizing repeatedly for the lengthy wait and exhaustive search the jail required me to submit to before seeing him. He was in good spirits. Bremner was, too. He was getting out soon. They would have a few weeks of freedom together before he went to Massachusetts, where he would serve the remaining six months of his sentence.