It was a simple message about a photo found in the ashes.
Elizabeth Stringer Keefe posted this message on social media every 9/11, hoping to find the people in the photo. But each year, nothing happened.
"I thought, 'Why not? I'm going to do it one more time everywhere.' And I saw it getting retweeted," said Keefe.
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And soon, the professor at Lesley University in Cambridge, Massachusetts, realized this time was different.
"I think a half an hour later, I knew it was going to happen," she said. "It was so exciting. I start to tear up when I think about it. It started to go viral, so I stayed up all night and just watched."
More than 6,000 tweets later, one message from Fred Mahe changed everything.
"He sent me a very cryptic message," said Keefe. "It just said, 'I know the people in the message, give me a call.'"
So she did.
"When he answered the phone, he said his name, and I said, 'This is Elizabeth Stringer Keefe,'" she said. "He paused for a minute and said, 'You are awesome.'"
A friend of Keefe found the photo at ground zero, just a few weeks after 9/11. Keefe made it her mission to find out the story behind it.
"I said, 'Are you in that photo?' And he said, 'That is my photo,'" said Keefe. "It was unbelievable, I immediately started crying."
Mahe worked in Tower Two. He had just come off the subway when the building was hit. The photo, taken at his friend's wedding, was tacked to his desk on the 77th floor.
Mahe now lives in Colorado, and all six people in the photo are alive and well.
"On 9/11, like you, I saw the worst of humanity. The absolute worst. But on 9/12, I saw the best," said Mahe. "And the photo mystery was solved on 9/12."
"Finding Fred, and being able to return this particular photo to him, is unbelievable," said Keefe.
Keefe and Mahe will meet for the first time Monday in New York.