David Quintavalle said he was bombarded with threatening calls after a protestor in the crowd hurled a fire extinguisher at U.S. Capitol police, hitting an officer, during the riots in Washington D.C last week.
WATCH: Full interview with retired Chicago firefighter David Quintavalle
While it was happening, Quintavalle said he was 700 miles away at home in Chicago. But an internet troll posted a tweet identifying Quintavalle as suspect. It picked up steam, and soon hundreds of others tweeted calling him a cop killer.
"It's out there," Quintavalle said. "I was a murderer, a terrorist. It changed everything."
Quintavalle said he's not on social media, but friends told him about the posts. He also got threatening phone calls, most of them similar to this: "Hey Dave you're a murderer and a traitor. And I can't believe you killed a cop and your son is a cop. Wow. Good luck in Prison."
"A police car had to be dispatched and stationed outside of their house," said John Nisivaco, Quintavalle's attorney.
Quintavalle has receipts from stores to prove he was in Chicago during the riots. He said he shaved his beard before Christmas, and without it he bears little resemblance to the real suspect.
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The FBI arrested 55-year-old Robert Sanford on Wednesday, charging him with attacking an officer who was not actually killed. But in the meantime, Quintavalle said his character and reputation have been trashed.
"The horse is out of the barn now," Quintavalle said. "Everybody in the world thinks I'm a murderer and a terrorist."
Quintavalle's attorney said his priority is to clear his client's name. But at some point in the future, he is looking to file a defamation suit against whoever started the tweets.