This case study presents a 10-year-old girl with a diagnosis of Autistic Disorder, who killed her 6-month-old sister by throwing her out of a window. Her aggressive-impulsive behavior had a persistent pattern. She had a history of epilepsy, and was frequently exposed to physical abuse. She never attended a structured treatment program. Here, we discuss the possible risk factors including history of epilepsy, unsupervised--disorganized home environment, existence of physical abuse--neglect and lack of appropriate treatment program leading to violent behavior.