After a state prosecutor charged that Pistorius "unlawfully and intentionally did kill" girlfriend Reeva Steenkamp, the sprinter entered a plea of "not guilty, my lady".Pistorius, 27, also pleaded not guilty to three unrelated gun charges. Entering the North Gauteng High Court on the opening day of the three-week trial , Pistorius looked nervous, dressed in a black suit and tie.Standing in the dock before a packed courtroom, Pistorius looked on as his lawyer Kenny Oldwage outlined the defence's case.