Mystery Man On Roof: Who Is It? And What Does He Have To Do With The Boston Marathon Bombing?

A Twitter controversy has erupted over a photo in which the figure of a man is seen to be walking on the roof of a building near the site of the second explosion at the Boston Marathon on Monday. Speculation has mounted as to who the figure is and what he might have been doing on the roof, with some suggesting that the figure might be a "lookout".

The photo was taken by spectator Dan Lampariello, according to Global News Desk, and depicts the second explosion at the Marathon from what appears to be hundreds of yards away. The wave of speculation was sparked after a parody Twitter account of musician Frank Ocean posted the photo along with the question, "Who's that guy on the roof?" The tweet was retweeted over 2,000 times. The user later attempted to play down the controversy by posting that the figure was a guard deployed for the Marathon.

One Twitter user called the photo of the man on the roof "the spookiest thing I have ever seen." Others questioned why the authorities weren't using the photo in their investigations, as well as why prominent media outlets weren't featuring the photo.

"I wonder if the FBI could look at cameras from that building to find the guy on the roof in the top left .." tweeted one.

This morning ABC News reported that at least 145 people were injured following the attack and that 17 of those injuries are critical. 3 people have died, including an 8-year-old boy.

This morning, the Massachusetts National Guard increased its presence in Boston from the 460 troops there at the time of the marathon to 1,000.

As of the time of this writing, no suspects had as yet been taken into custody as law enforcement agents continued a furious investigation into the events. A 20-year-old Saudi college student who was injured in the blast was questioned by the FBI in his hospital bed yesterday, but authorities emphasized that he was not a suspect, despite news reports claiming the contrary.

Security experts have also indicated that the bomb may have been concealed in a mail box of trash barrel, as suggested by the large pieces of metal shrapnel seen in one of the videos. They also say the bomb may have failed to function as planned, pointing to limited damage on nearby buildings.

Authorities also reportedly suspect that the bomb was a simple, low-velocity, explosive mixture, not that of military-grade weaponry.

In an address to the nation after the attacks, President Barack Obama vowed that authorities would find the suspect. "Make no mistake," he said "we will get to the bottom of this and we will find out who did this."