According to Osuna, DeFeo claimed that he had committed the murders with his sister Dawn and two friends, Augie Degenero and Bobby Kelske, "out of desperation" because his parents had plotted to kill him. Allegedly, DeFeo claimed that, after a furious row with his father, he and his sister planned to kill their parents and that Dawn murdered the children in order to eliminate them as witnesses. He said that he was enraged on discovering his sister's actions, knocked her unconscious on to her bed and shot her in the head. Police found traces of unburned gunpowder on Dawn's nightgown, which DeFeo proponents allege proves she discharged a firearm. However, at trial, the ballistics expert, Alfred Della Penna, testified that unburned gunpowder is discharged through the muzzle of a weapon, indicating that she was in proximity to the muzzle of the weapon when it was discharged and not that she fired the weapon. He reiterated this on an A&E Amityville documentary that is extensively discussed in Will Savive's "Mentally Ill In Amityville". Savive had an expert evaluate Della Penna's assessment and the expert confirmed that he was correct. Moreover, the medical examiner found nothing to indicate that Dawn had been in a struggle; the bullet wound was the only fresh mark on her body.