World's most Evil Killers - Diane Downs The World’s Most Evil Killers team of psychologists and criminologists examine the chilling case of Diane Downs, the Arizona born mother of three who murdered one child and left her remaining two critically injured. Arriving at a hospital in a bloodspattered car, Diane claimed that a car jacker had shot her and her three children. However, forensic evidence did not back up this story, and further statements made by her seemed strange and highly inappropriate. Investigators soon found she had developed an obsessive relationship with a former co-worker, and her surviving daughters testimony confirmed she had shot all three of her children in the car before shooting herself as an alibi.