On Dec. 28, 2014, Robert “Bobby” Smith shot police officer Tyler Stewart and himself in Flagstaff, Arizona. The video of that shooting has since taken on a life of its own. Police use it to talk about the dangers they face every day. Other people see it as a painful loop that will never stop playing. Follow Kelly McEvers and the show on Twitter @kellymcevers and @nprembedded. Email us at embedded@npr.org