By Kurtis Lee and David Kelly, Los Angeles Times (TNS) HIGHLANDS RANCH, Colorado — Students sprinting out of classrooms with hands clasped behind their heads. SWAT teams gripping rifles in the shadow of yellow school buses. Moviegoers slumped on the sidewalk, with popcorn strewn at their feet. These images are seared into the collective memory of the Denver metro area, home to some of the worst mass