Perth man to death was heard saying, “I’m glad I killed him, he’s a d**k”, a court heard.Robbie Smullen is accused of murdering 22-year-old Barry Dixon who died in hospital after receiving a stab wound to the heart.His mother, Mary Smullen, is in the dock alongside him accused of trying to cover up his alleged involvement.Both deny the charges against them and Robbie Smullen has lodged a special defence of self-defence at his trial at the High Court in Edinburgh.On Friday the court heard from