In the near-decade since the Boston Marathon bombing took the lives of three people and injured hundreds of others in 2013, many questions about the preventability of the tragedy remain. And now an upcoming documentary seeks to find the truth about a 2011 triple homicide that could shed light on the act of terror. The three-part event The Murders Before the Marathon, from ABC News Studios, Story Syndicate, and Anonymous Content, traces journalist Susan Zalkind’s investigation into the murders in Waltham, Massachusetts — a triple homicide committed exactly ten years after September 11 — and its possible connection to the Boston Marathon bombings. The trailer explores whether police incompetence and misconduct could have left the eventual suspect, Tamerlan Tsarnaev, free to commit the bombings with his brother, Dzhokhar Tsarnaev. Could Tsarnaev’s arrest have changed the course of history? Zalkind, who knew one of the Waltham victims, takes it upon herself to unravel the bombshell story about a procedural breakdown that could have prevented future tragedy. The documentary features exclusive details and new findings uncovered by the journalist to provide an in-depth look at the two events that may well be inextricably linked. The series premieres on Hulu on September 5.