THE intensive manhunt for the bombers behind the deadly Boston Marathon attacks didn't take place only on the streets with professional police officers and SWAT teams.
In an era of digital interactivity, it also unfolded around the country on laptops manned by ordinary citizens.
Fuelled by Twitter, online forums like Reddit and 4Chan, smartphones and relays of police scanners, thousands of people played armchair detective as police searched for men who turned out to be suspects Dzhokhar and Tamerlan Tsarnaev, ethnic Chechen brothers who had immigrated from southern Russia years ago.
As amateur online sleuths began identifying possible culprits, caught in the virtual manhunt were people who were wrongly accused or placed under suspicion by crowdsourcing.
It showed the damage that digital investigators can cause and raised a relevant question: In the social-media generation, what does law enforcement unleash when, by implication, it deputises the public for help?
"The FBI kind of opened the door," said Hanson Hosein, director of the University of Washington Master of Communication in Digital Media program. "It was almost like it was put up as a challenge to them, and they rose to it.
"They can be either really helpful or mob rule."
The bombings have been the highest-profile case in which the public has joined an active investigation, using ever-evolving crowd-sourcing tools, showing the pitfalls and benefits of new technology.
It's certainly not vigilantism, but it's not standard policing, either. It's something in the middle, perhaps something new - the law-enforcement equivalent of citizen journalism.
While listening to the police scanner, Reddit and Twitter users thought they had heard the name of a Brown University student missing since March, and one user posted a news story about his disappearance.
That assumption proved wrong - and there was a cost.
The missing student's family, besieged with ugly comments, temporarily took down a Facebook page asking for help finding him.
A few hours later, the online detectives said sorry - in the words of one moderator, "Rather Confused," for "any part we may have had in relaying what has turned out to be faulty information."
Several Reddit users who posted on r/findbostonbombers did not immediately return messages seeking comment.
The rush to informal sleuthing began on Monday soon after the smoke cleared as pictures and videos from the marathon began to circulate on the internet.
Salah Eddin Barhoum, a 17-year-old track star who was a spectator at Monday's race, had his picture posted all over the internet and ended up on the cover of the New York Post.
He told The Associated Press on Thursday that he is now afraid to leave his house.
Some of the amateur police work didn't sit well with the professionals.
Boston's police department, for example, has a very active Twitter account with more than 220,000 followers, but the onslaught of misinformation proved to be too much.
At one point, Boston police asked people to stop tweeting information from their scanner traffic.
While Reddit and 4Chan have been around for several years, their prominence has grown of late. More and more news organisations have learned to use them to mine information.
For Hosein, sub-sections on Reddit have become something like local newspapers, except it's the users providing the content.
"Citizens think they almost have an obligation to rise up to do the work," he said.
Hosein says that the FBI's call for help was no different than a "Wanted: Dead or Alive" poster from the 1800's - albeit with much more amplification and distribution. But he feels that after this week's saga, people will eventually learn to exercise caution.
"There's a sense that we're learning collectively quickly, that we actually have to take on some of the sourcing rules that journalists have had in the past," Hosein said.
