A segment of the leaked footage shows the Paralympian running without his prosthetic legs and pretending to hold a gun.
Another clip shows him carrying a woman out of a bathroom, watched and directed by several men in suits.
A third shows Pistorius, 27, on the floor of the bathroom, apparently demonstrating how he found his murdered girlfriend Ms Steenkamp, 29.
The video was due to be shown on the Sunday night documentary slot of Australia’s Channel Seven last night.
However, Anneliese Burgess, a spokeswoman for Pistorius, said the athlete’s legal team was “seeking urgent clarification” from the broadcaster about the footage, amid claims Channel Seven may have paid to obtain it.
His lawyer Brian Webber went on to say footage shown by Channel Seven was made with the help of a US-based company last year as part of the defence team’s trial preparations.
Wearing a green vest and black lycra shorts, Pistorius is impassive as he acts out the events of the night that, as he said in the witness box, “everything changed”.
He maintains he shot at the lavatory door thinking Ms Steenkamp was an intruder but the state says he killed her deliberately after an argument.
It is unclear for what purposes the re-enactment was prepared, or why it was not shown to the trial. The footage was filmed at the athlete’s uncle Arnold’s house in South Africa where he has been living since the shooting. Reports before the trial claimed an American firm called The Evidence Room was preparing an animated re-enactment of the events but no mention was made of it in court.
During his time in the witness box, Pistorius described how he woke in the night to move two fans in from the balcony and heard what he believed to be the bathroom window opening.
He said he believed an intruder was in his home, whispered to Ms Steenkamp to get down and call the police, then got his gun from beside his bed and crept towards the bathroom.
Pistorius said he heard the lavatory door slam and started shouting at the perceived intruder to get out of his house, while telling Ms Steenkamp to call the police.
He said a third noise from inside the lavatory prompted him to shoot at the door four times. Witnesses have told the court the Paralympian was unable to run on his stumps without holding on to something for stability, but the preview footage shows him running unaided.
Last week, a psychiatrist told the Pretoria court that Pistorius could not simply run away if he found himself in a vulnerable position. Even turning around is “quite a process”, he said, contrary to the Channel Seven footage which shows him able to move forwards and backwards unaided through the living room.
He shot Ms Steenkamp four times at his Pretoria home on Valentine’s Day last year.
The double amputee told the court he was convinced she was an intruder and that he fired his 9mm pistol accidentally out of fear and panic.
He said he went to investigate the noises coming from the cubicle before he fired.
Pistorius’ trial resumed last week after an adjournment so the Paralympian could undergo intense psychiatric evaluation.
The trial heard that Pistorius has a “split personality”, with a superstar status in front of the cameras and a private life as a disabled man.
His legal team said he was acting out of morbid fear, not anger, when he shot his girlfriend.
As the star’s trial draws to a close, his legal team has presented him as a vulnerable double amputee who battled great pain and genuine fears every day of his life, while the prosecution painted a picture of a volatile, gun-toting man.
Pistorius, whose running prosthetics have earned him the nickname the Blade Runner, denies murder and three firearms charges.
The trial resumes today.