Boston: Man on the roof

Abby Ohlheiser has a Slate article about the Boston bombing:

When nearly a day passes following a national tragedy like the Boston Marathon bombing without answers from authorities, not everyone is interested in leaving the investigation to the professionals. All the more so when Federal authorities are asking for anyone with photos from the event to send them their way.
Case in point: Boston's so-called "man on the roof" (photo).
The person in question— barely a silhouette on a rooftop captured in the background of a photo of one of the explosions— has sparked the imagination of countless Twitter users, not to mention at least one British tabloid that saw within the blurry snapshot a "chilling image" of a "mystery figure lurking on a rooftop".
Interest in the mystery man has grown so great that during a press conference, the FBI acknowledge that they were aware of it, although they declined to comment on the photo or any other images flagged by the public for investigators. "We are processing a lot of digital photograph evidence right now," FBI Boston Division head Richard DesLauriers said, before renewing his request that the public continues to submit any and all photographic evidence that may help authorities piece things together.
Spectator Dan Lampariello snapped the photo in question Monday and posted it to Twitter, where it then began to spread far and wide, a process that was accelerated by— no joke— a Frank Ocean parody account.
In case you haven't spotted the man in question yet: he's standing on a rooftop about two-thirds up from the bottom of the frame. Given that a roof deck would be an excellent place to watch the Boston Marathon finish line, there's nothing in the photo that indicates the man was acting suspiciously. Even in the zoomed-in versions of the photo, you can't see his face; his reaction is likewise nearly impossible to judge in the still photo (as are the reactions of those actually running the race).
Nevertheless, the British tabloid The Sun has run a bit wild with speculation:

This chilling image shows a mystery figure lurking on a rooftop, as a bomb blast rips through the Boston Marathon finishing line below. The person does not seem to react as the ground-floor of the building erupts into flames following the second explosion. It was not immediately clear whether the figure on the roof had anything to do with the terror attack. But some claim it raises the unnerving possibility that a perpetrator watched on as the street-level carnage was unleashed.

Rico says that the guy's not doing a very good job of 'lurking'...