(CNN) On September 11, 2001, amid the burning ashes of the World Trade Center, three New York City firefighters hoisted a small American flag removed from a nearby yacht. It was 5 p.m. on a day that would radically change the course of history.
The image, captured by a former photographer from The Bergen Record, became a symbol of hope and resiliency in the face of unimaginable tragedy.
But within hours of its raising, the flag disappeared from the World Trade Center site.
The iconic flag is now back in New York City, 15 years after it went missing.
It will be displayed near the entrance of the National September 11 Memorial and Museum, built on the site of ground zero.
Its reappearance is as mysterious as its disappearance.
CNN film traces disappearance
The mystery of what happened to the ground zero flag was the subject of a 2013 CNN film "The Flag."
Iconic image of 9/11 flag raising
Firefighters George Johnson, Dan McWilliams and Billy Eisengrein raise a flag at ground zero in New York after the terror attacks on September 11, 2001. The scene was immortalized by photographer Thomas E. Franklin. The image has been widely reproduced in the decade since it was first published. View 25 of history's most iconic photographs.
The now-famous photograph was never featured on the front page of The Record, the newspaper Franklin works for in Bergen County, New Jersey. The photo appeared on page 32 on September 12, 2001.
On September 13, 2001, the front page of Britain's "The Sun" draws the comparison between the image at the World Trade Center and Joe Rosenthal's 1945 photograph of U.S. troops raising a flag in Iwo Jima during World War II.
Newsweek features Franklin's photo on its cover on September 24, 2001.
Firemen re-create the flag raising during the 2001 World Series in Phoenix, Arizona, on October 27, 2001.
A firetruck that features a mural depicting a firefighter raising the flag is unveiled to the public in Clintonville, Wisconsin, on January 20, 2002. The truck was donated to the New York Fire Department.
The scene captured by Franklin also made its way onto a commemorative coin.
Artist Jim Conrad designed a sculptured bronze version of the flag raising in honor of the Rev. Mychal Judge, a New York Fire Department chaplain who lost his life while administering last rites on September 11, 2001. Conrad is seen polishing the sculpture in 2002 at his home in Lakewood, Colorado.
President George W. Bush unveils a "Heroes of 2001" stamp issued by the Postal Service on March 11, 2002, to raise funds to assist the families of emergency relief workers killed or permanently disabled as a result of the World Trade Center attacks. He is joined at the White House by the firefighters who are featured in the image, from left, Eisengrein, Johnson and McWilliams.
The stamp is displayed at a ceremony outside of the Brooklyn Borough Hall in New York on July 2, 2002. From left, Brooklyn Postmaster Joseph Lubrano, Borough President Marty Markowitz and Harold Meyers of the New York City Fire Department were in attendance.
NASCAR driver Jamie McMurray decorated the hood of his car with a replica of the "Heroes of 2001" stamp. A crew member helps ready the car at the Daytona International Speedway in 2002.
The image can also be found on T-shirts, like this one worn by Venita Bradford at a memorial service in Energy, Illinois, on September 11, 2002.
A version of the photograph appears on a commemorative knife.
A snow globe owned by collector Josef Kardinal depicts the flag raising at ground zero. He is seen in 2006 at his home in Nuremberg, Germany.
A 40-foot-tall bronze monument named "To Lift a Nation" depicts the famous scene. Pictured at a warehouse in 2007, the sculpture is now part of the permanent collection at the National Fallen Firefighters Memorial Park in Emmitsburg, Maryland.
A woman holds a commemorative plate at her home in San Salvador, El Salvador, on September 7, 2011.
The iconic image has also been turned into a pair of earrings.
Wax figures of the firefighters are displayed during the "HOPE: Humanity And Heroism" exhibition at Madame Tussauds in Washington on May 10, 2013.
Photographer Thomas E. Franklin sits at his work station in Hackensack, New Jersey, in 2002.
The original flag was "either misplaced, stolen or secreted away by unknown forces in the chaos of ground zero," according to Michael Tucker, who produced, wrote and directed the film with his wife, Petra Epperlein.
When an official was sent to pick up the original flag a week or so after 9/11, he apparently received a larger flag which was flown at subsequent events, the film's director said.
That was the flag that flew over Yankee Stadium during a 9/11 Prayer Service on September 23, and fluttered over the USS Roosevelt as the aircraft carrier sent missions over Afghanistan.
Original flag turns up mysteriously
The original flag eventually resurfaced in Everett, Washington.
A man who only identified himself as a retired Marine named "Brian" turned it over to a local fire station in November 2014.
The only other information Brian gave was that he had been given the flag on Veterans Day 2007 by a man who had received it from the widow of a 9/11 firefighter, said Everett Deputy Police Chief Mark St. Clair. Brian then vanished.
Among those who died on that fateful day were 343 firefighters.
Everett detectives launched a search for Brian. They even released a sketch of him to the local newspaper in the hopes that he would be identified and could provide more helpful information about the flag. However, their efforts proved futile.
DNA discovered on electrical tape on the flag's halyard did not match DNA from any of the three firefighters who raised the flag on 9/11, or the owners and crew of the yacht where the flag had initially flown.
Forensic tests confirm authenticity
At the Washington State Patrol laboratory, forensic scientist William Schneck spent weeks analyzing photos, the flag's fibers and thousands of dust particles -- comparing them to a pure sample of World Trade Center dust taken from a New York City fire truck at ground zero.
The composition of "pulverized building material" was a match. According to the lab report, the flag and its accompanying ropes had been exposed to the World Trade Center dust cloud in September 2001.
"We wanted to be thorough and complete and be able to have the investigation stand independently," said Everett Detective Jim Massingale, a retired Army Ranger. "We knew it would be scrutinized."
A retired New York Police Department officer who now works with the Everett Police Department held the flag as it was being packaged to return to New York City.
"He actually grabbed onto that flag, held it up to his face and smelled it, and turned and looked at me and said, 'That's the smell that I remember from that day,'" said Detective Michael Atwood.