>> it's mark cassie, he is the assistant district attorney. >> reporter: coming up. >> mark, come on. the ambulance is coming. it's almost here. >> reporter: a dedicated prosecutor shot, right outside the courthouse. stunning onlookers and police. >> it's nothing you could prepare for. >> reporter: who would even attempt such a brazen attack? >> did that tell you that they knew each other? >> it seemed personal to me. >> reporter: when "dateline" continues ♪ ♪ no matter how you stay fit keep it light with light & fit's rainbow of delightful, protein-packed flavors. ♪ ♪ beyond the routine checkups. beyond the not-so-routine cases. comcast business is helping doctors provide care in whole new ways. all working with a new generation of technologies powered by our gig-speed network. because beyond technology... there is human ingenuity. every day, comcast business is helping businesses go beyond the expected. to do the extraordinary. take your business beyond. . ♪ >> reporter: a beloved prosecutor, mark cassie had been shot outside the courthouse in kaufmann texas during the morning rush.