Who is this person? Individual seen walking on roof directly overhead as bomb goes off at Boston Marathon

A picture posted on Twitter shows an individual walking on the roof directly overlooking one of the blasts at the Boston Marathon.

The picture of the mystery person was posted shortly after the terror attack and raises the eerily possibility that one of the perpetrators watched as the carnage was unleashed.

Law-enforcement sources told the New York Post that a 20-year-old Saudi man was detained at a Boston hospital.

Fox News reported that suspect was badly burned.

He was taken into custody less than two hours following the 3 p.m. blasts that have killed at least two people and injured dozens more.

It was not immediately clear whether the person on the roof had anything to do with the terror attack.