“The whole country now has been deputized — they’re essentially law enforcement without being sworn in,” Eugene O’Donnell, a professor at John Jay College of Criminal Justice in New York and a former New York City police officer and prosecutor, said in an interview.

The readiness of authorities to mobilize the public’s help in finding the culprits was “unprecedented and probably forms the model going forward for high-profile cases,” O’Donnell said. “For like-minded people who might be planning violent activities, this is not good for them. There’s nowhere to run, there’s nowhere to hide.” …

A bombing victim helped authorities narrow down the sought- after images from hours of video: Jeff Bauman saw a man who dropped a bag that exploded minutes later, and his description delivered from a hospital bed helped investigators, according to his brother, Chris Bauman. …

“What the Internet has done is take the idea of the wanted poster in the post office and elevated it exponentially,” Robert Thompson, a professor of television and popular culture at Syracuse University in Syracuse, New York, said in an interview. “It’s one thing to canvass a neighborhood. The Internet allows that canvassing to reach such a wider range.”