cutors say Sierra suffocated all three victims with yellow plastic Sedano's shopping bags. They also allege that he sexually assaulted Machado and Julia after their deaths. The jury is now weighing whether Sierra should receive a life sentence or the death penalty. During opening statements Tuesday , prosecutors described the killings as  heinous, atrocious and cruel.  The defense acknowledged the  horrific  nature of the evidence while asking jurors to consider Sierra's background and the effects of a traumatic childhood brain injury on his personality and executive functioning. Defense attorneys have said Sierra suffered a severe head injury in a childhood car accident that affected his cognitive functioning and personality. The penalty phase is expected to continue with additional testimony and evidence before jurors make a recommendation on the sentence.