UK Daily Mail 
April 16, 2013
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.