For years, officials wondered what happened to an emotional symbol of September 11th. Today, that mystery is now solved, and the flag that had gone missing is now back at the World Trade Center site. NY1's Michae; Scotto filed the following report.

The photo is one of the most iconic from September 11th. It shows three firefighters raising the American flag at the World Trade Center site hours after terrorists destroyed the towers. 

"The raising of this flag restored some humanity. It restored some hope," said Joe Daniels, president and CEO of the National September 11th Memorial and Museum.

Soon after the photo was taken, the flag vanished - gone, the city thought, for good.

But then in 2014, the History Channel ran a program about the mystery. Within days, a possible break. Someone brought a flag to a firehouse in Everett, Washington nearly three thousand miles away.

After a lengthy investigation, complete with forensic tests, experts confirmed that it was the missing stars and stripes, a finding that was announced this week.

Brad Meltzer, the host of the show that led to the recovery, is overwhelmed by his role in resolving the mystery. 

"I'm still in shock. I still feel like, 'How's this possible?'" Meltzer said.

The flag has been placed on permanent display at the 9/11 Memorial and Museum.

"The whole idea of this flag not being in this museum, having this essentially a mystery for years and years and years about where was the Ground Zero flag, just felt like a hole in the history of this site," Daniels said.  

One mystery still remains: how the flag disappeared and ended up across the country.  

Detectives from the Everett Police Department have not been able to find the man who returned the flag.

Scotto: So he returned the flag and disappeared.
Jim Massingale, former Everett police detective: Disappeared. That's correct.  

The flag became synonymous with September 11th after firefighters had taken it from a yacht docked at the World Financial Center and hoisted it over the rubble. 

Shirley Dreifus and her late husband owned that boat.

"I never expected to be part of history. And I never expected this to happen. And I never expected the flag to be found," Dreifus said.

But now, it has been found and is back at the place where it first brought hope.