KABUL, Afghanistan—A prominent doctor was kidnapped and killed in northern Afghanistan, his family said Saturday. Mohamed Nader Alemi was abducted two months ago in the city of Mazar-i-Sharif, and his kidnappers demanded a ransom for his release, his son Roheen Alemi said. The family eventually paid them $350,000, after negotiating down their initial demand of more than twice that, he said. Despite the payment, the kidnappers then killed Alemi, leaving his body in the street, his son said. They called the family and told them where to find it on Friday, he said. “My father was badly tortured, there are signs of harm on his body,” Roheen Alemi said. Alemi, a psychiatrist, worked for the government’s provincial hospital in Mazar-i-Sharif. He also owned a private clinic, said to be the city’s first private psychiatric clinic. The Taliban Interior Ministry spokesman, Saeed Khosty, said Taliban forces arrested eight suspected kidnappers who …