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DENVER -- Each September since the 9/11 attacks, Elizabeth Stringer Keefe has tried to solve a mystery.Shortly after the attacks, a friend gave Keefe a wedding photograph she found at Ground Zero. The torn photo shows a bride and groom beaming alongside four guests. Keefe's friend never learned who the photo belonged to, or if the people in it were even still alive.

But Keefe, a professor in Boston, just couldn't let it go, The Australian reported.

She has been searching for more than a decade, posting the image online to see if anyone recognized the couple. No one did.

Until this year.

@ProfKeefe @reddit please message me. I know someone in the photo. Thank you. — Jason (@gramercy17) September 12, 2014

After more than 60,000 shares, one of Keefe's tweets led her to Fred Mahe, a Colorado native who worked in the World Trade Center. The photo was his, taken at a friend's wedding. He's the man on the far left of the image.

@TakinADigg It is my picture that was at my desk on the 77th Fl of WTC Tower 2. The picture has been kept safe by @ProfKeefe for last 13yrs — Fred Mahe (@FredWMahe) September 13, 2014

Mahe, who now lives in Erie, Colo., was out of the office on 9/11. He confirmed that all six people in the photo are still alive and that the newlyweds now live in California and no one in the photo was hurt in the tragedy.

“It was an overwhelming conversation," Keefe told The Boston Globe. “Every year I go dig it out. I’ve been posting it for years, and it’s literally never gone anywhere.”