This case report present an 8 years-old girl with a diagnosis of Autism Spectrum Disorder (ASD), who killed her 9-months-old brother by throwing him out of a window. Children with ASD exhibit various externalizing behaviors including harming others. A combination of poor emotion regulation and impaired understanding of others’ emotions is associated with aggressive behavior in children with ASD. Her aggressive-impulsive behavior had increased during the last 1 year. Here, we discuss clinical picture and possible risk factors leading to violent behavior in this subject.