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.
Who is this individual walking on the roof overlooking the blast? This picture posted to Twitter shows somebody standing directly above the scene of the carnage
Fox News reported that the suspect was badly burned.
He was taken into custody less than two hours after the 3pm blasts that have killed at least three people and injured more than 140.
It was not immediately clear whether the person on the roof had anything to do with the terror attack.