As government investigators in Boston and around the country have been working to follow the winding stream of forensic data and digital imagery toward the terrorist behind the Boston Marathon bombing, a parallel investigation has been happening, completely in the open, on the Internet.

At the head of this decentralized, distributed investigation are the sprawling yet insular communities of Reddit, the self-proclaimed “front page of the internet” and 4chan, a prominent Internet subculture imageboard. (Reddit is owned by Advance Publications, the parent company of Condé Nast, which is the publisher of The New Yorker.) Gathering at “subreddits” like “findbostonbombers,” a horde of amateur digital forensic analysts have been poring over every pixel of some of the same raw material as investigators—publicly available high-resolution photos and video of the race, bombing, and aftermath, which has been scattered across the Web and broadcast by news media—hoping to see something that official investigators have not. It’s a human-powered parallel-processing machine, one with overwhelming scale that is constantly churning as it aggregates known information with new data, synthesizing the two to produce highly idiosyncratic analyses. The machine is marked by its intensity, heterogeneous composition, and its odd syntax, in which annotations are made with crude graphics, and arguments are made in the raw language of Internet forums.

The Internet collected its first two chief suspects early yesterday. The first, “Blue Robe Guy,” is a white bearded man wearing a navy-blue fleece and a red T-shirt, who, in annotated photos, is carrying a backpack on his forearm in an awkward way. The pack appears similar to the shredded one in photos released by the F.B.I. He is already an Internet meme. Another, dubbed “Suspect #1” in an imgur post called 4chan ThinkTank, is a man of unknown ethnicity with dark skin and short, nearly buzzed black hair, wearing tan cargo pants and a black jacket. He’s also carrying a similar black backpack. By late yesterday, following a news report, attention had shifted to a pair of men—one with with a white hat and black backpack, and another in a blue track outfit carrying a blue Nike bag—that officials had requested help identifying, one of whom had been discussed previously on the forum. A series of images, annotating the men’s proximity to “ground zero,” along with analysis of the weight of their bags (noting how much they sagged) shortly followed from Reddit’s /r/findbostonbombers on imgur.

These open excavations are operating at the center of a deep tension between notions of public and private, particularly on Reddit, which, for starters, prohibits posting personal information, like real names or addresses. There is also a self-awareness about the potentially tragic consequences of identifying the wrong man—for a time, the top post on Reddit’s /r/findbostonbombers recalled the story of Richard Jewell, the security guard accused, then cleared, of committing the Olympics bombing in Atlanta, in 1996. Yet, these communities believe that, despite conducting their investigation in a fully public space—/r/findbostonbombers has well over three thousand subscribers, while 4chan’s ThinkTank image dump has over a million views—they should be able to operate within a vacuum, insulated by their higher purpose. They think that they should be able to talk about suspects freely inside this private space, without worrying about their chatter affecting real people in the real world (until they decide it should, of course). The Reddit user who created /r/findbostonbombers, Oops777, insists in an interview with BuzzFeed, that “things shouldn’t be going any further than this forum and the FBI,” while chastising media outlets for “already playing the ‘who done it’ game themselves,” stating that “it is obviously dangerous when done by a paper [or] TV outlet.” The top post now, from Oops777, pleads: “Media Outlets, please stop making the images of potential suspects go viral, then blaming this small subreddit for it.” He adds in the post that there is “a list of rules to stop ‘witch hunts’”—as if the rules of an online forum have power in the real world, which has itself been turned upside down. Another user posted a comment, “Slate is claiming this ‘amateur sleuthing’ can do real damage…then why is slate providing links directly to the “Blue Robe Guy” sub??? Nice attempt at damage control!!” Yet one Redditor claims that the man in the blue track outfit’s Facebook page has been found, where he was defending himself from accusations. These actions have consequences, even on the Internet. According to Deadspin, which viewed his Facebook profile before it was made private, he is a high school track athlete.

Those contradictions seem mindboggling—insisting on insularity in a forum watched by thousands, attempting to identify a target without actually making that person a target. But this friction is a useful form of doublethink, providing these Internet communities with the best of all possible worlds: If their allegations are incorrect, they can declare that they never intended to mark a man, that it was the media’s doing; if Blue Robe Man or White Hat Guy prove to be behind the bombing, an arrest will be hailed as a triumph of the power of the Internet and crowdsourcing, which would be touted as rivaling or outstripping traditional forensic investigation.

This moment is, for better or for worse, the shape of things to come. What’s new and incredible is the scale and speed of this machine. It seems like there will never be another event like the Boston bombing that isn’t endlessly teased apart and put back together again in this way. Thanks to the ubiquity of inexpensive, powerful digital-imaging devices creating unimaginable amounts of data, and the emergence of highly populated, highly distributed Internet communities like Reddit and 4chan, it will happen this way every single time. It will happen in full view of the Internet; it will be insanely fast; it will be messy. That process might not always produce the answers we want—the right ones, for instance—but it’s increasingly hard to disbelieve that one day it will.

Above: F.B.I. crime-scene investigators in Boston on Wednesday. Photograph by Darren McCollester/Getty.

Read more of our coverage of the Boston Marathon explosions.