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Boston Marathon blast witnesses turn to social media

Two bombs exploded near the finish of the Boston Marathon on Monday, killing two people and injuring at least 99 others. About two hours after the winners crossed the line, there was a loud explosion on the north side of Boylston Street, just before the photo bridge that marks the finish line. Another explosion could be heard a few seconds later. Competitors and race volunteers were crying as they fled the chaos. Bloody spectators were being carried to the medical tent that had been set up to care for fatigued runners. Authorities went onto the course to carry away the injured while stragglers in the 26.2-mile race were rerouted away from the smoking site.

April 15, 2013 12:00:00 AM PDT
News of the bombings at the Boston Marathon on Monday spread quickly over the Internet.

Just moments after the explosions, videos and pictures of the horror began to appear on social media. The Images that instantly showed the magnitude of the attack made the terror and fear palpable.

Social networks were filled with conversations, with celebrities like LeBron James and Paula Abdul offering sympathy to victims. People on Twitter were also urging television networks - and fellow tweeters - to show caution in what they were reporting to avoid inflaming the situation with false details.

The "#PrayForBoston" hashtag was trending for hours on Twitter.

Across the U.S., security was tightened at landmarks, government buildings, transit hubs and sporting events. Law enforcement agencies also urged the public via Twitter and Facebook to report suspicious activity to the police.

Google set up a person finder website to help family and friends of runners or those at the marathon to find who they were looking for.

The Associated Press contributed to this report.