PROVIDENCE, Rhode Island/LISBON, Dec 19 - A quarter of a century ago, Claudio Neves Valente was briefly enrolled as a young, promising doctoral student in the physics department at Brown University before dropping out of the school in Rhode Island.

On Friday, police were still trying to figure out why Valente returned to the Ivy League school nearly a week ago, armed with at least one handgun. He killed two students and injured several others before fleeing from the building where he once studied.