Amir Bar-Lev’s documentary The Tillman Story investigates the mysterious circumstances surrounding the death of Pat Tillman, an N.F.L. player who quit football to join the Army Rangers and was killed in Afghanistan in 2002, and his family’s years-long battle with the U.S. military to learn what really happened. Krista Smith spoke to Bar-Lev at the 2010 Sundance Film Festival, where the movie premiered.