In a 45-year career, much of it spent in the front ranks of news photographers, he worked for The Associated Press, Time and Parade, covering 13 wars and amassing about 500 photojournalism awards. But it was a 1968 photograph from Vietnam, taken for The A.P., that cemented his reputation in the public eye and among his peers. That black-and-white image captured the exact moment that Brig. Gen. Nguyen Ngoc Loan, then serving as the national police chief of South Vietnam, fired a bullet at the head of a Vietcong prisoner standing an arm's length away on a Saigon street.