Retired Col. Benjamin H. Purcell of Clarkesville, who was the highest-ranking Army POW in Vietnam, died Tuesday at age 85. Purcell, an alumnus of the University of North Georgia and a former professor of military science and commandant of cadets at the school, served in the U.S. Army for more than 30 years. A native of Clarkesville, he held command and staff positions from platoon leader through brigade commander, including combat tours in Korea and Vietnam.