A few years ago, while scouring a Fresno, Calif., antiques shop, Randy Guijarro coughed up $2 for three old photographs. Now, one of those images—said to be the second verified picture ever found of outlaw Billy the Kid—is worth an estimated $5 million.

In the shot, the Wild West gunslinger is holding a weapon of a different variety: a croquet mallet. Henry McCarty (a.k.a. William Bonney, a.k.a. Billy the Kid) plays the unexpectedly dignified sport alongside members of his gang The Regulators in the summer of 1878 in New Mexico. The 4-inch-by-5-inch tintype was authenticated by a firm called Kagin’s Inc.

Guijarro had no idea he’d procured a valuable piece of American history until after he brought it home and realized that one of the men looked like Billy the Kid. It took more than a year to authenticate the image.

Guijarro told National Geographic:

“... It’s almost a Twilight Zone photograph. That’s why it’s caught so much attention, skepticism, and pushback. You have the most famous and iconic American around the world, posing on a croquet stick with the Regulators, along with his girlfriend. This is a story. It’s not just a portrait of him. This tells a day in the life.”

It’s a remarkable find, considering there’s only one other known photo of the thief and gunfighter in existence.

If you’re itching for more on the Wild West legend and the recently recovered photo, you're in luck. On Sunday, October 18, the National Geographic Channel will air a documentary about Guijarro’s efforts to authenticate the image.