I would speculate if there were three individuals with bombs, that they were positioning themselves to detonate the bombs when the crowds left the stadium. In Israel suicide bombers sometimes looked to work crowded streets at night. In this case whatever their plans were, were frustrated when a bomb detonated prematurely.
This happened right before halftime when a lot of people normally leave the stadium. Today I heard it was locked down after the explosion -- didn't know that until after we left the stadium.
Never thought of that until you mentioned it. He was within yards of the stadium since it happened at Cross.