Amateur sleuths have taken to the Internet in an effort to find out who planted the deadly bombs that exploded Monday at the Boston Marathon, uploading photos from the moments before and after the explosions and analyzing them for clues on who may be responsible.

Federal officials have asked spectators to send in any photos they may have from the day’s events.

But some are conducting their own guesswork on who set off the bombs that killed three and injured 176 Monday afternoon.

Advertisement - Continue Reading Below

At the website Imgur.com, dozens have uploaded their snapshots of the crowd close to the 26-mile marker, with circles and arrows marking what they consider shifty-looking spectators and ominous black backpacks that online commenters speculate could be the key to the investigation.

Users of Reddit, 4Chan, craigslist and other sites have already taken it upon themselves to crowdsource the investigation: Reddit’s /r/findbostonbombers/ forum already has almost 800 members and has highlighted suspicious persons and objects through collected photographs and videos, the Globe’s Michael Morisy reports in his Inside the Hive innovation blog.

But the top-voted item on that page is a cautionary reminder: It notes the case of Richard Jewell, the police officer and Olympic security guard falsely accused of planting a bomb at the 1996 Summer Olympics in Atlanta, Morisy writes in the item, “The Social Fog: Sorting through the endless Boston Marathon data, together and alone.”