In the week since 18-year-old University of Virginia sophomore Hannah Graham mysteriously disappeared while walking home late at night, police have canvassed her neighborhood and interviewed her friends. Her parents have called for the Fairfax County native’s safe return. Her classmates have massed and mourned.

And amateur Internet sleuths, never ones to miss out on public tragedy, have taken some action of their own: watching and rewatching online surveillance videos, creating maps of Graham’s every suspected move … and gradually coming up with a few original theories.

“I believe Hannah was taken into the garage,” proffered one man on Facebook. “I highly think the older man and the dreaded head man are in this together.”

“Let police know the second man is in this tape,” another guy writes on YouTube. “Black big dude with dreads clearly following her.”

“It is entirely possible” that Graham’s disappearance is linked to other local disappearances, one Redditor writes in a forum dedicated to discussing serial killers. “Besides being female and missing, what other similarities are there that the victims share? Age, race, profession, etc.?”

This is, for better or worse, what a high-profile crime investigation looks like in 2014: constant media hype, breathless real-time “analysis” and veritable Everests of Internet speculation. The story has repeated enough times, in fact, that it’s no longer a novelty. Whenever police release surveillance photos or videos to the public, they can count on the Internet to edit, squint at and otherwise overthink them — generating hundreds of theories and tip-line calls in the process.

Just days ago an anonymous Twitter sleuth earned the praise of Philadelphia — and its police department — when he identified several suspects in a brutal hate crime. Using Facebook’s Graph Search function and tips from other Twitterati, the account @FanSince09 discovered not only clear pictures of all the suspects, but the names of several in the group.

“This is how Twitter is supposed to work for cops,” detective Joseph Murray tweeted. “This is what makes my job easy.”

But often, of course, social media doesn’t work that way — and while cases like the one in Philadelphia have emboldened and encouraged Internet sleuths, their actual record is spotty. In April of last year, a group of well-intentioned Redditors in the forum r/bostonbombings compiled thousands of videos from the scene of the Boston Marathon bombing, studying them for suspicious backpacks and bystanders.

“It’s been proven that a crowd of thousands can do things like this much quicker and better,” the forum’s moderator wrote at one point. “I’d take thousands of people over a select few very smart investigators any day.”

Except that every “suspect” the forum identified was wrong — complicating the actual FBI investigation and damaging the reputations of several innocent people. When Redditors attempted to launch a similar forum six months later, this one tied to the Navy Yard shootings, site administrators promptly shut it down.

The hacktivist collective Anonymous has likewise become notorious for its attempts to “seek justice” in a number of national cases — but to Anonymous, “justice” has frequently meant poorly researched, vigilante-style revenge. The group correctly identified a number of high-schoolers involved in Steubenville’s infamous rape case and surfaced critical photos and videos from the scene. But when Ferguson, Mo., police failed to immediately release the name of the officer who shot and killed Michael Brown, Anonymous hackers released his name — and address, and Social Security number — themselves.

They had the wrong guy.

This doesn’t mean that crowd-sourced sleuthing is necessarily bad or that law enforcement should discourage it. On the contrary, in cases like Graham’s disappearance, police are often hoping to reach as many potential witnesses and tipsters as possible, and the efforts of 20,000 avid Facebook users can only help get their message out. The last “major break” in the case, in fact, came from public tips: Multiple callers drew police to a condo, and a car, in an apartment complex off the U.Va. campus.

This, in fact, may be the critical red line between “good” Internet sleuths and “bad”: The former work to help actual investigators; the latter want to be the investigators, themselves. It’s a subtle bit of hubris that explains the yawning ethical and efficacy chasm between calling a tip in to police, say, and calling the suspect or witness directly.

In Hannah Graham’s case, it may be the difference between sharing police updates and news releases, and engaging in long, unqualified analyses of the same. Even as I write this, armchair detectives on Facebook and YouTube are demanding to know why police haven’t arrested the “dreads guy” — a man with dreadlocks seen in two surveillance videos who was conclusively ruled out as a suspect.

“I really believe this to be the man they are looking for,” one woman posted on Facebook with a surveillance still of the “dreads guy.”

“I just don’t think there’s a way to tell from the video,” another man replied. “We’ll know that when the police tell us.”

It’s good advice, not only in this case but in most freelance investigations that Internet sleuths get into.

(Note: This article has been updated.)