Phil Coale / AP

After the twin towers fell, three firefighters hoisted a 3-foot-by-5-foot flag up a lanyard above ground zero and a photographer captured the moment. The Associated Press picked up the photo, as did Newsweek, and countless other media outlets. It became a stamp and a symbol.

Twelve days later, Rudy Giuliani, at the time the New York City mayor, signed the flag at Yankee Stadium. It was also signed by his successor, Michael Bloomberg, and by New York Governor George E. Pataki. It would travel to naval ships in the Middle East, and in 2002 it returned to City Hall. Except the flag that had been signed and did all the traveling was not the flag pictured in the photo, the one raised in the hours after the September 11 attacks. For starters, this flag was 5 feet by 8 feet. So what happened to the original flag?

That remains, in part, a mystery. But on Thursday, the original flag, verified by forensic scientists, goes on permanent display at the National September 11 Memorial & Museum in New York.

How the flag became lost and how it reappeared is a somewhat unsatisfying story, because there are so many unanswered questions. What’s known is it showed up at a fire station in Everett, Washington, in 2014, four days after the History Channel featured an episode on its disappearance.

The flag had originally belonged to a New York couple who’d hung it from the back of their yacht. One of the firefighters in the photo had taken it from the vessel and hoisted the flag above the rubble of the towers. In 2014 the History Channel’s Brad Meltzer asked for help solving the mystery in an article he wrote for The Huffington Post. In it, he said, they’d found a clue, which led to another dead end. Meltzer wrote:

On the night of 9/11, a New York police officer was shooting surveillance footage at Ground Zero. In this footage, at 10:30 p.m., the famous flagpole from the photo is bare. The flag is already gone, meaning that it had already been taken down within five hours of the iconic photo.

To this day, New York City has no leads, nor does the FDNY. Some experts suggest the real flag was misplaced at Ground Zero in the days after 9/11. Others suggest it was stolen. Others guess it may have been used to cover the body of a slain first responder and therefore could be stored in a morgue.

A week later, Meltzer’s episode on the mysterious disappearance of the ground zero flag ran on the History Channel’s spinoff, H2. Apparently, someone in Everett, Washington, was watching, because four days later a flag was dropped off at a fire station by a man named Brian.

“At least that’s what the firefighters recall him using,” Mark St. Clair, the deputy chief of operations, told The New York Times. The man said he was a former Marine, the Times reported, and that he’d been given the flag by someone at the National Oceanic and Atmospheric Administration, who had been given the flag by a widow of a September 11 victim. That story has been called questionable.

Regardless of how the man came to own the flag, firefighters told the local police, and investigators looked into the claim that this flag, which was 3 feet by 5 feet, was the original featured in the iconic photograph.

The flag was turned over to a Washington State Patrol Crime Laboratory forensic materials scientist who, as the Times reported, analyzed dust samples on the flag and compared them with those taken after the towers fell. They matched.

There still remain questions, like who took it from the pole in the five hours after the September 11 attacks? And  how did it end up on the other side of the country?

But Thursday the flag returns home, and that much is true.

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