Sean Hackett, the 19-year-old former captain of Tyrone GAA's minor football team, shot his father Aloysius dead in January last year.But Dungannon Crown Court has heard the accused told detectives he had been mentally ill at the time.Prosecution lawyers on Tuesday have been opening the case against the teenager.Ciaran Murphy QC revealed that on 4 January 2013 Aloysius Hackett's body was discovered close to his Citroën Xsara car in a yard at the rear of his home on Aghindarragh Road.Mr Hackett had just returned from a meeting at the GAA club in Augher.The prosecutor said as Mr Hackett was getting out of the car he was shot by his son Sean, and he managed to move a few feet before collapsing and dying.Mr Murphy said the accused had obtained the murder weapon from a friend. It was a .22 bolt-action rifle made in the Czech Republic and capable of firing high-velocity bullets.The lawyer said Sean Hackett fired three bullets in total, with two them hitting his father in the side of the head. Death would have been fairly rapid.Mr Murphy said Sean Hackett had fired single bullets, ejecting the empty cartridges and re-loading to fire again. He said the defendant had the presence of mind to pick up two spent cartridges and remove them from the scene.He added: "This was a crime he planned. He obtained the weapon and clearly knew how to use it accurately despite the horror of what he saw the first shot was fired, and despite the horror of what he was doing to his own flesh and blood, to his own father."Mr Murphy said Sean Hackett drove to a neighbour's home and told them something had happened to his father. But within hours he confessed to the shooting.During an interview with police he gave detectives a prepared statement that said: "Last night I was involved in an incident that led to the death of my daddy whom I love very much. In recent months I have been suffering from depression for which I have been seeking medical treatment."The trial continues.