A suburban Minneapolis community was in mourning on Monday after authorities said two police officers and a firefighter were killed by a heavily armed man who shot at them from inside a home that was filled with children. The shooting on Sunday in a tree-lined neighborhood of Burnsville, Minnesota, left a third officer wounded. Minnesota Bureau of Criminal Apprehension Superintendent Drew Evans said there was an exchange of gunfire, and authorities were still piecing together details of what he described as a “terrible day.”