A crowd mostly composed of college students gathered at the Parkman Bandstand on Boston Common late Sunday evening to celebrate the death of terrorist Osama bin Laden. Two days ago, President Barack Obama announced that bin Laden was killed by a joint ground operation of the Navy SEALs and the CIA. The crowd sustained itself for almost two hours with an ebullient atmosphere, chanting and occasionally singing. Police officers stood nearby to monitor the energetic gathering. The students seemed to be predominantly from Boston University and MIT, with sparser showings from other area colleges.