South African prosecutors yesterday sought to show Oscar Pistorius' sports doctor overstated his immobility without prostheses, as a leaked video shows the star sprinter re-enacting the shooting of his girlfriend. State prosecutor Gerrie Nel took Wayne Derman to task about his claim the athlete was mentally vulnerable and had limited mobility on his stumps. Pistorius' defence team says both factors led the Olympian to shoot Reeva Steenkamp in the early morning hours of Valentine's Day 2013 out of fear that she was an intruder. Nel's tough questioning came as a haunting video of the 27-year-old star sprinter was aired by The Seven Network, an Australian television network. In the video, Pistorius, wearing a blue tank top and tight black shorts, is walking on his bare stumps with his arm outstretched and hand clenched as if aiming a pistol. In another clip, Pistorius walks backwards on his stumps, appearing to cast doubt on the defence claim the runner has limited mobility without wearing his prosthesis. "Can I just ask you then was it ever demonstrated to you that Mr Pistorius was able to walk backwards on his stumps?" said Nel. "It was never demonstrated to me," said Derman. Nel worked to show that Pistorius wilfully moved towards the bathroom to shoot his girlfriend Reeva Steenkamp four times with a 9mm pistol. "There was at least an option for the accused to flee, even walk out of the room, am I right?" said Nel, suggesting that Pistorius was criminally negligent by choosing to shoot instead of leaving his bedroom. The leaked video was made by the Evidence Room, a US company that specialises in forensic animation. Lawyers for the athlete said it was commissioned by his defence team and obtained illegally by the TV station. But the Australian television network defended its decision to run the footage, insisting it was not obtained unlawfully. "We would not have run the footage if we thought we had obtained it illegally," said Mark Llewellyn, executive producer of the Sunday Night programme. Pistorius' team warned against any other media rebroadcasting the clip. The network said it had broadcast the footage only in Australia. However, it did not say how it obtained it. Legal observers say it is unlikely that the prosecution will be able to introduce the video as evidence.