Apparently convinced they could supplement the FBI’s Boston marathon investigation, Internet vigilantes on Reddit, 4chan and other online message boards began their own crowdsourced sleuthing shortly after midnight on April 17. But as annotated photos from the scene went viral, some of the self-styled sleuths seemed to back off their quest — noting, as many critics had already, that vigilante meddling could hurt innocent people.

“You may get lucky and your pet suspect turns out to be the bomber,” reads a warning post on the Reddit thread “findBostonbombers.” “But I’ve seen at least 10 people singled out, and not all of you are correct. You should be very very careful about picking and choosing who you think might have killed three people and wounded many more, based on where they were standing and if they were carrying a backpack or not.”

In many cases, that type of circumstantial “evidence” is all the hivemind is running on. One man, dubbed the “blue robe guy,” has been flagged repeatedly on Reddit for holding a black and silver backpack over one arm, rather than on his back.

Two of Reddit’s other favorite “suspicious males” are noteworthy, commenters write, because they have a backpack in some early photos, and do not seem to have it in others. They also appear to be of Middle Eastern or African descent, a fact not lost on vigilantes.

On 4Chan, one user posted an aerial photo from the marathon with bold red text superimposed over one man: “1: ALONE 2: BROWN 3: Black backpack 4: Not watching,” it says.

Reddit users eventually noted that the man in question might not have been watching because he — like other men on the scene wearing black jackets, khaki pants and army boots — could have been law enforcement. And there are, notably, at least five other people carrying black backpacks in the very same frame.

As Will Oremus notes over at Slate, this type of crowdsourcing, as futile as it looks, has proven effective before. Last year, for instance, a Redditor identified the make and model of a car involved in a hit-and-run after looking at a photo of its right headlight.

But vigilantism could also have very serious consequences, both for the innocent people whose photos are now annotated all over the Internet, and for the ongoing investigation itself. Reddit appears to have woken up to the fact: Shortly after 1 p.m., the “findBostonbombers” forum added a thread to confirm people as innocent. That followed a moderator’s post that listed new rules for the amateur sleuths.

Among the regulations: Do not post personal information. Do not make any images go viral. Do not speculate. For the Internet hivemind, those could be hard rules to follow.

“Isn’t this all about speculation?” One user wrote. “I’ve read through quite a few posts here and this entire subreddit seems to be nothing but speculation. When you wrote this rule what were you thinking of that is not speculation that would be ok [sic] to post?”