There’s no doubt that the road to capturing the Boston Marathon bombers was paved with crowd- sourced data. When the FBI and the Boston Police launched what may have been the largest crowd-sourced manhunt ever undertaken, they probably didn’t know how much investigative information they were to receive.

Asking tens of thousands of people to send their photos was a big gamble. Imagine the volume of digital images they had to comb through? And asking for tips from the public could have (and may have) unleashed a monster, with reams of information pouring in, much of it not very helpful. With crowd-sourced photos, digital footage from video surveillance in the area and thousands of tips, managing the evidence would have been a mammoth task.

But it worked, and it worked quickly. Within hours law enforcement officers knew who they were looking for and it helped them track the Boston bombers down pretty efficiently. One of the reasons it worked so well is that people believed in what they were trying to do. They were on the side of the “good people”.

The Dark Side of Crowd-Sourcing

But all the news around the investigation wasn’t positive. There were stories of innocent people being misidentified as the bombers, even by media outlets that were doing their own crowd-sourcing.

At one point, missing Brown University student Sunil Tripathi was reported to be a suspect, sparking a witch-hunt that made headlines and prompted an apology from Reddit’s general manager Erik Martin, who wrote: "The Reddit staff and the millions of people on Reddit around the world deeply regret that this happened. We have apologized privately to the family of missing college student Sunil Tripathi, as have various users and moderators. We want to take this opportunity to apologize publicly for the pain they have had to endure."

Speculation and Confirmation Bias

Crowd-sourcing can lead to dangerous speculation. When people jump to conclusions they may not only identify the wrong person, but once they believe they have the culprit, they may unconsciously interpret evidence to support their belief.

It’s called “confirmation bias” and, according to investigation experts, it’s a dangerous mistake and can lead to a wrongful conviction. It occurs when people make a decision about a case either beforehand or too quickly and then they look for facts that line up with their theory, filtering out contrary information without even realizing it. Because it’s unconscious it’s even more dangerous. And crowd-sourcing that leads to premature conclusions by people who don’t have any investigation experience can be harmful.

Crowd-sourcing, just like any other investigative tool, must be used responsibly and precisely to be effective.