Protesters demonstrated Friday for a third day over the fatal police shooting in Pennsylvania of an unarmed black teen fleeing a traffic stop as they sought to get the attention of a nation engrossed by the immigration debate, and to pressure officials to charge the officer.

Hundreds of marchers chanting "Who did this? The police did this" shut down a Pittsburgh area highway in the early morning hours, and a small group staged a sit-in outside the district attorney's office later in the day.

Demands for answers to why a police officer shot 17-year-old Antwon Rose Jr. seconds after he bolted fr...