"Kill or Be Killed" reveals the stories of those who lost their lives at the hands of someone they knew, who then claimed it was self-defense. In these complex cases, the lines between murder and justifiable homicide are blurred, making them some of the hardest cases to solve. When the killer is the best and sometimes only witness, investigators must scrutinize every other detail. Law enforcement, prosecutors and defense attorneys unravel every detail, from the harrowing stories, forensics, interrogations and witness statements that led up to the gruesome event in order to find answers.