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.