Over the last 12 hours, hundreds of people have made posts on the forum. Users have superimposed images of bombs over backpacks, questioned hand gestures and bag-carrying techniques, and constructed elaborate theories for spectators' behaviors: Why is he looking that way? Where did his shoulder bag go? Have we considered strollers? The leading suspect in the subforum right now is "Blue Robe Guy," a man with a backpack that faintly resembles the one recovered from the bomb wreckage. (His face is clearly visible in many of the photos, some of which were taken a full three hours before the bombs went off.)

Oops777, who did not share his real name, is not from Boston. He's a 23-year-old professional poker player from England. "Reddit has some really good update threads for all the news from the Boston bombings," he says. "People were already speculating on suspicious people in the crowds, I found something very weird which is the first post I made [in the subreddit]." The post, called "Two suspicious Males," traces two bag-carrying men through various photos of the marathon crowd. "The worst case scenario is we waste our time," he says, "but the best is that we find something the FBI missed — which is why all suspicious information that isn't ruled out, is sent to the FBI."

What you'll be seeing are the results of a large, distributed, and loosely organized investigation into the Boston bombings by strangers on sites such as Reddit and 4chan. And to the extent that the investigation has a leader, it's this guy: Oops777, a Reddit user who created /r/findbostonbombers/. The forum has over 1,000 subscribers and, at the time of writing, had nearly 2,000 simultaneous viewers.

If you spend much time on the internet today, you'll probably see at least one example of the following: a photo of the crowd near the finish line of the Boston Marathon, taken moments before the blast, annotated with red arrows, scribbled outlines of pressure cookers, or photos of different brands of backpacks. Despite their content, the images will bear a striking resemblance to popular memes.

Official investigators are likely examining some of the same data right now and asking many of the same questions. But they're doing so behind closed doors, while Reddit is doing it in the most public way possible. Oops777 maintains that the purpose of the subreddit is to forward information to the FBI, not to spearhead vigilante campaigns. "Reddit itself, and us specifically, prohibits any posting of personal information whatsoever," he says. "If anyone was to post something other than a picture that could be used to identify somebody then they will immediately be banned."

The prohibition on publishing private data is official Reddit policy, but it's up to moderators (and a few official administrators) to enforce it. And the site's images, along with 4chan's, are going viral. They may not contain names or addresses, but they contain faces and strong suggestions of guilt. "That is a shame, things shouldn't be going any further than this forum and the FBI," says Oops777. "Unfortunately media outlets are already playing the 'who done it' game themselves," he adds, "which is obviously dangerous when done by a paper [or] TV outlet (see Daily Mails report on the bombings - they have multiple 'who's this guy' pictures)." He believes by consolidating the information in one subreddit, it can be more effectively vetted. "I think I'm going to post something in the forum to try and keep users from spreading anything outside of the forum," says Oops777.

Functionally it's hard to find any distinction: A popular post on Reddit will have identical consequences to a story on the front page of a news site — it will be seen by as many, if not more, people. And in both cases, suggestive images will be stripped of context and shared with a vigilante subtext. If "roof man" could capture people's imaginations, consider the potential response to Oops777's first post, which noted "suspicious" behavior by two young men of West Asian or Middle Eastern descent. It's possible – likely, even, given the sheer number of attempts — that when we find out the true identity of the bomber, it will be one of the people highlighted in these images. But perhaps more importantly, it won't be one of the dozens more implicated. And it seems exceedingly unlikely that 4chan's images will be the cause of an arrest.

Other users are wary. "Is this a case of 'guilty while Arab?'" wrote one in response to Oops777's post. "I mean, there are a lot of backpacks in that crowd... Just saying, lets not miss something because we're trying to use racial profiling to find a terrorist here." Oops777 responded: "That's not remotely true, essentially all large black backpacks are being looked into."

It's also easy to imagine, should a true suspect emerge, a shift in tone. Compelling images that aren't officially addressed, or relevant to any official investigation, could easily become fodder for conspiracy theorists, who won't stop until they know who "Blue Robe Guy" really is. Early reports of an impending arrest suggest that a suspect was found using security footage, which would not be publicly available.

To the forum's credit, the top-voted post on the forum is a link titled "Does anyone remember Richard Jewell?" Jewell was a security guard whose discovery of a pipe bomb at the 1996 Summer Olympics likely saved lives, but who was aggressively portrayed as a suspect by the media based on flimsy reports. He was eventually and fully cleared, and won settlements from many of the outlets that covered him, including CNN.

But it's a post made in vain: This is part of the process now. People, their skepticism attenuated by shock and grief, are eager to do something. And, for better or for worse, this is what that looks like.

Update: The FBI released this statement on Wednesday afternoon: