It had been a long time since anyone had asked about the outlaws, and Señor Cranky Pants wasn’t eager to show me their room. But, finally, the desk clerk at the crumbling El Globo hotel, in Trelew, Argentina, snatched some keys off a hook and led me to the cramped quarters where Butch Cassidy and the Sundance Kid had, it was said, once stayed when they were in Patagonia, taking a stab at being legit ranchers.

The brass bed was not even queen-size, but the man insisted that in it had slept not just the two men but also their hermosa compañera, Etta Place, circa 1905. As Butch himself no doubt said on more than one occasion, “Whoa.” The clerk said, “Dos hombres, una mujer, and shrugged theatrically.

The Wild Bunch, an outlaw gang of bank and train robbers, was led by Butch Cassidy, seated right. Seated left is Harry Alonzo Longabaugh, otherwise known as the Sundance Kid.

I drew two lessons from that hotel visit. One was that, more than a century after they rode into the sunset, Butch and his pals were still inspiring admiration, bemusement, and envy. The other was that once again the real lives of these people proved more interesting than they’d seemed in the 1969 movie, in which Butch (Paul Newman) took Etta (Katharine Ross) for a chaste bicycle ride to the tune of “Raindrops Keep Falling on My Head” while Sundance (Robert Redford) was off doing cowboy stuff.

South and West

For four years I tracked Butch through the American West, Manhattan, Brooklyn, Argentina, and Bolivia with a growing sense of relief. To write a life of any prominent outlaw is to court disaster. You begin with the shiny celluloid version of a famous bandito and, as a reward for all your fine ferreting, often wind up with a drunken pimp. With Butch, though, the reverse occurred. The longer I followed the footsteps of the man born Robert LeRoy Parker, the more I realized he was every bit as charismatic as the character played by Newman—and also much more intriguing.

Dos hombres, una mujer.

Butch played by rules that he never wrote down but followed strictly. The most important was to never hurt anyone physically or even financially. When the train passengers or bank customers who got caught up in his crimes held out watches and wallets, Butch told them to put those things away; he wanted only what was in the company safe. Cattle barons, railroad magnates, and bankers were fair game for Cassidy, but not the regular folks scraping by in the arid, corporately controlled West. Was he a Robin Hood? No, but he did spend his spoils like a heavyweight champ, and his money often found its way into the households of the needy and the garter belts of dance-hall girls, helping the local economy. “Butch took care of more people than F.D.R. and with no red tape,” one of his girlfriends later said.

Paul Newman, Robert Redford, and Katharine Ross in Butch Cassidy and the Sundance Kid.

Why didn’t screenwriter William Goldman, who won an Oscar for the movie, portray Butch as the populist hero that he truly was? For the same reason he turned Sundance into a quick-draw artist: Goldman was not writing history but, in the time-honored Hollywood tradition, making stuff up. He refused to be “constrained by facts,” he said, and when I looked through his papers at Columbia I found in the movie folder only a 1950s Butch Cassidy comic book and scattered notes. Newman did no research whatsoever, but he wound up falling for his character, and for the rest of his life haunted rare-book and manuscript shops, searching for what he said was “the only thing I want that I don’t have: Butch Cassidy’s autograph.”

Charles Leerhsen’s Butch Cassidy: The True Story of an American Outlaw is out now from Simon & Schuster