Leading national and local politicians as well as some 1,500 family, friends and supporters commemorated the police officer who was stabbed to death by an Afghan immigrant a week ago in the south-western German city of Mannheim. German President Frank-Walter Steinmeier described the knife attack in which a police officer was fatally injured on the city’s Market Square as a “bloody act of terrorism.” The mother of police officer Rouven Laur, 29, broke down in tears. Laur died on Sunday, days after he was injured as he sought to intervene when a man attacked several people during a rally by the …