CHICAGO — David West was 9 years old when Phillip Pannell — an African American teenager in his Teaneck, N.J., neighborhood — was shot in the back and killed by a white police officer, triggering a night of racially charged violence in the streets near West’s house. As the story became a fixture on the national news, West struggled to reconcile the friendly 16-year-old who had waved at him while walking by West’s house a couple of times a week with the neighborhood ruffian being portrayed on his TV screen.