A Tennessee teenager on trial for murder says he killed his mother with a sledgehammer because she knew he had been raped by his older brother and did nothing about it. Zachary Davis was fifteen when he bludgeoned his mother's skull 12 times as she slept and then set his family home ablaze in an effort to also kill his elder sibling Josh. On Tuesday, a court in Hendersonville heard how Davis, now 17, laughed as he killed his mother Melanie Davis in August 2012, leaving her bloodied and unrecognizable before fleeing. Davis is charged with first-degree murder, attempted first-degree murder and aggravated arson and the court was shown gruesome images of the crime scene as his trial began on Monday. According to prosecutors, Davis, his mother and brother went to see the comedy movie, The Campaign on August 10 and then returned home. Melanie Davis went to sleep at 9pm, 'not knowing that her younger son was planning something sinister, something unspeakable.' In testimony given to the court by Major Don Linzy, Chief of Detectives at the Sumner County Sheriff's Office, Davis confessed after he was apprehended at a convenience store eight miles away, having fled the scene. 'Yes, sir, I killed my mom in her sleep with a sledgehammer,' Linzy told the court on Tuesday according to the Tennessean. Linzy said that during his interview Davis was asked why he killed his mother with a sledgehammer and replied, 'I was worried that I'd miss,' and that using that type of weapon gave him the 'highest chance of killing her.'