Sen. John McCain said Friday that he considers the death of American Kayla Mueller by Islamic State militants one of the saddest moments of his life as he looked back on his work in trying to secure her freedom and the government's policy of not paying ransom to terrorists.

McCain discussed the Mueller saga during a news conference in Phoenix after a week that saw him take a spot on the national defense stage yet again following the confirmation of Mueller's death. McCain, himself a prisoner of war during the Vietnam War, worked to get Mueller set free over the last 18 months after she was captured in Syria in August 2013.

Mueller was captured after accompanying her boyfriend on a trip to the country.