SEATTLE (AP) - An American doctor working in Botswana was killed by a crocodile that pulled him from his canoe. The family and colleagues of Doctor Richard Root say it happened Sunday during a wildlife tour after visiting a clinic. The crocodile reportedly thrust from the water, grabbed Root, and pulled him under. He was not seen again. Root was 68, and a medical professor at the University of Washington. He moved to Botswana to ease a doctor shortage, and was training health care workers to deal with AIDS. Root was a nationally known expert in infectious disease.