FERGUSON, Mo. — Dorian Johnson had just moved from his mother’s house in St. Louis to a two-bedroom spot in the Canfield Green Apartments that he was sharing with his then-pregnant girlfriend and another roommate. Sometime in March, a buddy stopped by with a stranger. “Wow,” Johnson said, “that’s a big dude.” The dude, Michael Brown, was 6-foot-4, and he had brushed past Johnson with barely a hello as he headed to the video-game console and began to play. “I asked, ‘Why he don’t speak?’ ” Johnson recalled in a 90-minute interview with The Washington Post last week — his first...