supporters protested on the steps of the hall of justice this afternoon demanding district attorney george gasgon file charges against the officers who shot and killed emile lopez in the mission district, armed with a knife. they held signs that said 679 days marking how long it's been since his death. >> this is enough. >> enough is enough. >> reporter: on the same day less than five miles away police chiefs and captains from across the country including san francisco gather to talk about police accountability and use of force. >> obviously hot button issues with law enforcement nationwide. >> reporter: san francisco interim police chief tony chaplain says body worn cameras or a welcome addition. >> it's also a piece for the officers falsely accused of things they didn't do. >> reporter: cell phone videos of officer-involved shootings changed the landscape. >> the police department needs and wants the support of the communities that we serve. >> reporter: captain dan perreia of the mission station shared a recent interaction he had with a 16-year-old mission high school student. >> the one quest