Federal investigators are combing through a number of leads in the Boston Marathon bombing case, including a surveillance image of a man putting down a backpack near one of the bombing sites, captured before the blasts.

Meanwhile a couple of news and image-sharing websites, Reddit and 4Chan, have been overrun with users trying to do their own parallel investigation. Amateur digital-forensic analysts are going through much of the same data as investigators, circling suspicious people in backpacks and swapping theories about who did it and how.

These people want to solve the case, and maybe they can, but in the crude world of internet crime-solving, could they be doing more harm than good?

Joining us to explain is Alexis Madrigal, Senior Editor at The Atlantic.