A 23-year-old man wielding an assault rifle and carrying 100 rounds of ammunition shot and killed a Transportation Security Administration officer at Los Angeles International Airport on Friday morning, sending travelers fleeing in panic and paralyzing one of the world’s busiest airports for hours.  Two other people, one of them a security agent, were shot and at least four others were injured in the melee. The gunman entered Terminal 3 just before 9:3o a.m., pulled a weapon from a bag...