WASHINGTON - Protesters are expected to gather in Washington for a huge demonstration on Saturday, its police chief said, as U.S. street marches over the killing of a black man in custody enter a 12th day and authorities move to rein in policing tactics. Some activists on social media have called for a million people to attend a protest in the capital. “We have a lot of public, open source information to suggest that the event on this upcoming Saturday may be one of the largest we’ve ever had in the city,” Washington DC Police Chief Peter Newsham told local...