The Marathon bombing changed Boston. It also changed Twitter.

Dan Lampariello was one of the first people to share a photo of the Marathon bombing, taken from where he was standing on Boylston Street.John Tlumacki/Globe Staff

Before the runners were stopped, before the wail of ambulances and the cascade of grief, before the manhunt got underway, it was a photograph posted to Twitter from a Suffolk University student that alerted the world of something bad at the Boston Marathon.

“Explosion at coply,” said the misspelled tweet from Dan Lampariello, posted at 2:50 p.m. on April 15, 2013, just one minute after the bombs went off. The photo of Boylston Street, taken on Lampariello’s iPhone 5 one block from the finish line near Copley Square, captured the plume of smoke from the first blast and the fireball from the second.

Explosion at coply pic.twitter.com/EqKbGeWhha

— Dan Lampariello (@DanLampNews) April 15, 2013

“That was the platform that I’m like, ‘I gotta get this out, let people know what happened down here,’ ” Lampariello, whose post quickly went viral, recalled in an interview. “It was the fastest way to reach as many people as I could.”

His was among the first of the 27.8 million tweets sent about the bombings over that fateful week. Just as it was a watershed moment for Boston, so, too, was it for Twitter, a communication platform uniquely suited to convey updates at crisis speed, reflecting the web of confusion, fear, and mourning in 140 characters or less.

Spectators such as Lampariello — who is now an investigative journalist in Portland, Maine — used Twitter to transmit eyewitness accounts. Law enforcement posted public safety information and updates to the investigation. Journalists around the country scoured feeds for on-the-ground sources. The Marathon bombings helped cement Twitter’s role as an interactive town square, giving users a place to amplify public safety resources, seek out places to take shelter, and connect with loved ones after phone lines jammed. Twitter was where the healing spirit of #BostonStrong flourished.

“The Boston Marathon bombing showed that Twitter could be a place to experience life as it was happening,” said Emily Dreyfuss, a senior editor and research fellow for the Technology and Social Change Project at the Harvard Shorenstein Center on Media, Politics and Public Policy. “Twitter became a one-stop shop to process social trauma.”

Ten years later, Twitter is a juggernaut better known for other things, many less flattering: Elon Musk’s takeover, controversial policy changes, and staffing issues. But one legacy of that April day is the ubiquity of social media, especially in helping people find and share information in critical moments.

Just as the JFK assassination transformed television news and 9/11 underscored the necessity of cellphones, the Marathon bombing helped usher in a new, enduring tech standard: When disaster strikes, turn to Twitter.

To be sure, Twitter, which debuted in 2006, had already crashed the geopolitical stage with movements such as the Arab Spring and Occupy Wall Street. But the Marathon bombing coverage drove home the real-time nature of Twitter, with people tracking every twist and turn on a platform that put all voices on equal footing, said Dreyfuss.

“It made people realize that if they went there for their news, then they’re also participating in the news,” she said.

But Twitter’s participatory nature also paved the way for the waves of misinformation that would beset social media in the years to come. Internet sleuths took to Twitter and Reddit to circulate half-baked conspiracy theories, such as the one that missing Brown University student Sunil Tripathi was one of the attackers. In a study done months after the bombings, researchers found that 29 percent of the most viral tweets during that time period were rumors or otherwise false content.

For the Boston Police Department, however, Twitter became a way to cut through the noise. Shortly after the explosions, then-commissioner Ed Davis called Cheryl Fiandaca, who was the chief of the Bureau of Public Information at the department. “We’ve got to start putting this information out and letting people know what’s going on,” Fiandaca recalled Davis telling her.

Boston Police confirming explosion at marathon finish line with injuries. #tweetfromthebeat via @CherylFiandaca

— Boston Police Dept. (@bostonpolice) April 15, 2013

Within an hour, BPD confirmed the explosions on its Twitter account. From there, the BPD account was staffed 24 hours a day, Fiandaca said, posting safety instructions for civilians, information on the police response and the ensuing manhunt, and updates on casualty counts. The department also tried to counter misinformation as it arose, such as the false claim that an arrest was made on April 17. (The number of followers on the department’s account ballooned from about 40,000 before the bombing to more than 300,000.)

When Dzhokhar Tsarnaev was captured in a boat in Watertown four days after the bombings, the first official confirmation came in the form of an exclamation-laden tweet from BPD.

“It had never been used before, obviously, during a crisis in the way that it had been for this,” said Fiandaca. “It became the gold standard.”

Cheryl Fiandaca (left) was one of the people ringing the opening bell for Twitter at its initial public offering on the New York Stock Exchange on Nov. 7, 2013. Fiandaca was the chief of the Bureau of Public Information at the Boston Police Department during the Marathon bombings, leading the department's robust Twitter response to the tragedy. REUTERS

Many reporters, too, found a conduit to information on Twitter, using it to amass eyewitness accounts from a scattered group of bystanders. Bill Kole, who was the New England bureau chief for the Associated Press, had watched the Marathon that morning but returned home to Sagamore by the time the bombs went off. He jumped on Twitter to try to find sources and eventually connected with Bruce Mendelsohn, a former Army medic who had rushed down to Boylston Street to treat the wounded. Kole continued to rely on Twitter during the manhunt, when a citywide shelter-in-place directive made on-the-street sources harder to come by.

Serri Graslie, who was a producer for NPR’s “All Things Considered” in Washington, D.C., first found out about the bombings from Lampariello’s photo. She then monitored Twitter for updates, creating lists of relevant accounts and searching for tweets from bystanders using geolocation information. From then on, Twitter shaped every aspect of how NPR approached the news, Graslie said.

“It was a moment where things switched,” she said.

Meanwhile, much of the rest of the region — and the country — leaned on Twitter for information and support. An image showing phone numbers for police tips or to get in touch with loved ones gained steam through retweets. People such as Back Bay resident Adam Amundson used the platform to open up their homes to anyone who might need a hot shower, warm food, or a cellphone charger. Alison McQuade, a Springfield native who was following her brother’s progress in the Marathon from her home in Washington, D.C., used Twitter to search for updates after her brother’s tracker stopped working.

“When anything like this happened, having a community around you is so important,” said Sarah Pekala, who volunteered at the starting line in Hopkinton that day. Twitter, she said, “made you feel a little bit more like you were together in it.”

Since that April, the influence of Twitter has grown expansively. In the last three months of 2013, Twitter averaged about 240.9 million monthly active users; in the final three months of 2021, the most recent full year for which data is available, there was an average of 217 million users per day. The platform has amplified political movements, fueled #BlackLivesMatter and #MeToo, and kept people connected during COVID-19 lockdowns.

But even today, the decisive shift that the Marathon bombing represented for Twitter looms large.

Two huge explosions just went off at #bostonmarathon finish. Cops running.

— Will Ritter (@MrWillRitter) April 15, 2013

Two minutes after the bombs went off, Will Ritter, who at the time was a press secretary for a political candidate and was near the finish line when the bombs went off, tweeted out, “Two huge explosions just went off at #bostonmarathon finish. Cops running.” On the eighth anniversary of the bombing, Ritter retweeted that post and got a response from J. Peter Donald, who had been a spokesman for the FBI’s New York field office at the time. Donald informed Ritter that his tweet “was the Bureau’s first notification to the Boston bombing— before scanners, radios and the press.”

Before the Marathon, Ritter said, Twitter was “like a chat room for my friends.”

“After that, it was like, ‘Wow, something you write can go absolutely global in seconds,’ ” he said. “And there’s no putting the genie back in the bottle.”