In 1971, a mysterious individual slipped into the museum at Valley Forge and nabbed a rare Revolutionary-era long rifle on display. Now, almost 50 years after the gun’s disappearance, the F.B.I. has located the stolen artifact and returned it to its rightful owner, the Pennsylvania Society of Sons of the Revolution (PSSR).

The five-foot-long flintlock rifle is no ordinary firearm. Johann Christian Oerter, a master gunsmith who produced high-quality weapons for American rebels out of his Pennsylvania workshop, crafted the firearm in 1775. Per a statement from Philadelphia’s Museum of the American Revolution, arms scholars cite Oerter’s work among the “finest and most important” of the colonial period.

As Jeremy Roebuck reports for the Philadelphia Inquirer, antiques dealer Kelly Kinzle happened upon the stolen rifle at a barn sale in Berks County, northwest of Philadelphia, last year.

“I actually thought it was a reproduction,” says Kinzle. “My first inclination was that it had to be fake, because the real gun isn’t going to show up in a barn in today’s world. Things like that are already in collections.”

After purchasing the gun and realizing its potential historical significance, the dealer contacted his attorney, who linked the weapon to the Valley Forge theft. Upon discovering the rifle’s true provenance some 13 months ago, Kinzle handed it over to the F.B.I.

According to Roebuck, F.B.I. investigators and local law enforcement have spent the months following the gun’s return attempting to track down the original thief. Kinzle, for his part, says he doesn’t think the previous owner—who he classifies as a hoarder rather than a collector—had anything to with the robbery.

Authorities presented the rifle, which will soon go on view in the Philadelphia museum’s “Cost of Revolution” exhibition, during a ceremony held last week.

As Karen Zraick reports for the New York Times, the still-unidentified culprit stole the rifle while it was on loan from the PSSR to the Valley Forge Historical Society, a direct predecessor of the American Revolution museum. The society had placed the artifact on view in the visitor center at Valley Forge State Park, which marks the site where George Washington’s army spent the brutal winter of 1777 and 1778.

Shortly after opening on the morning of October 2, 1971, the thief used a crowbar or comparable tool to pry open what was believed to be a burglar-proof case. Several hours later, a Boy Scout touring the museum alerted staff that the gun was missing.

Authorities waited several weeks to alert the public of the gun’s theft. Their rationale for delaying the announcement, according to the Inquirer, was fear that the thief would panic and destroy the rifle upon learning it was insured for more than $15,000—around $95,000 today.

At the time, investigators’ efforts failed to yield any promising leads. Local police and the F.B.I. reopened the case, which they suspected could be connected with a rash of thefts in the Valley Forge area during the 1960s and ‘70s, in 2009, but they made little progress prior to Kinzle’s chance discovery.

“It is deeply gratifying to be able to return this rare artifact to public view after nearly fifty years,” R. Scott Stephenson, the Philadelphia museum’s president and CEO, says in a press release. “The Christian Oerter rifle exhibits exemplary early American artistry and is a reminder that courage and sacrifice were necessary to secure American Independence.”

Pennsylvania long rifles like the one recently recovered afforded the Continental Army a “considerable military advantage” during the Revolutionary War, Ryan Thomas notes for the Pennsylvania Center for the Book. Used primarily for hunting, the guns had a technological advantage over British weapons—a twist inside the barrel that gave them extra accuracy and range. Thanks to long rifles, colonial sharpshooters were able to practice guerilla warfare, hiding in the trees and shooting targets from afar.