Pretoria, South Africa (CNN) -- Oscar Pistorius was on the stumps of his amputated legs when he knocked down a locked toilet door with a cricket bat to reach his shot girlfriend, a police forensic expert said Wednesday, countering the track star's assertion he was wearing his prosthetic legs at the time.
South African police colonel J.G. Vermeulen took the stand to discuss marks on a cricket bat and a bent steel plate found in the bathroom door after the athlete shot model Reeva Steenkamp on Valentine's Day last year.
Wielding the cricket bat in his hands, Vermuelen squatted down before swinging it at the actual wooden door in a court reconstruction to show the angle of the marks. He said the location of the spots on the door was consistent with Pistorius not wearing his prosthetic legs.
"From the forensic evidence, he was on his stumps," Vermeulen said.
Defense attorney Barry Roux countered by suggesting that even with his prosthetic legs on, Pistorius would not be swinging a bat at the same height as an able-bodied person.
In a change from his bail hearing, when the state based its case for a premeditated murder charge on Pistorius having had his prosthetic legs on when he fired the shots, the prosecution said Wednesday he was on his stumps during the shooting and when he bashed down the door. The track star has said he didn't have his prosthetics on when he shot at the toilet door after hearing a noise, but then put them on when he tried to break open the door, realizing his girlfriend may be inside.
The door is being used in the Pretoria court to show the trajectory of the bullets fired at Steenkamp, which both sides can use to argue whether it was premeditated murder or not.
Pistorius, the first double-amputee to run in the Olympic Games, regularly wears prosthetic legs. If he was not wearing them at the time, the trajectory of the bullets would be lower and the defense can argue that he was feeling vulnerable and didn't have time to think.
The 27-year old has pleaded not guilty to murder in the shooting. He admits killing Steenkamp, 29, by shooting her through a locked bathroom door in his house. However, he says that he mistook her for a burglar in the middle of the night and that the shooting was a tragic mistake. Pistorius has said he tried to break open the door when he realized he'd shot Steenkamp.
Door in focus
The court heard that the door was intact before the shots were fired.
Under cross-examination, Vermeulen said the first and only time he went to the crime scene was on March 8, 2013, nearly a month after the shooting. Asked about a mark on the door which he did not investigate, he said it was not from a cricket bat.
Roux asserted it was the mark of a prosthetic leg kicking the door with a sock on and that fabric remained in the mark on the door. Vermeulen was unwilling to accept that that was the only possible explanation.
Vermeulen told the court there were footprints consistent with police shoes on the bathroom door at one point and photos of this were shown. They were later removed and Vermeulen said he did not know how. He said that from photos, he knew the door was removed from its hinges and left on the floor for some time.
When Roux suggested they were wiped off by someone who did not know the importance of police procedure, Vermeulen chuckled.
Close-up photographs of the damaged door were shown in court, as well as scuffs on the autographed cricket bat, prompting a Tweet from former South African test cricketer Herschelle Gibbs: "Just saw my signature on the bat used by the accused in Oscar trial...lol".
Pistorius, who took notes and drew sketches during the testimony Wednesday, covered his eyes with his hand when a photo of a panel of the blood-spattered door was shown.
Friend: Pistorius sped, fired
Before the scientist testified, a friend of Pistorius who was with him twice when guns went off in the South African track star's hands was back on the stand to testify against him.
Prosecutors trying to convict Pistorius of murdering his girlfriend have charged him as well with breaking gun laws on both occasions.
The incidents were not connected to the fatal shooting of Steenkamp, but prosecutors appear to be using them to demonstrate that Pistorius is not safe around guns.
He grinned and shook his head as his friend, Darren Fresco, testified that Pistorius had been speeding during an incident that ended with the track star firing a shot out of the sunroof of a car.
Fresco said Pistorius was driving about 200 kilometers per hour (124 mph), but it turned out that a photo of the speedometer taken during that drive shows Fresco was driving. He said Pistorius was "furious" that police had touched his gun and later fired a shot out the sunroof.
The two men had been pulled over for speeding.
Fresco also testified about an incident at Tashas restaurant in which Pistorius is accused of asking him to take the blame for firing Fresco's pistol under a table a month before Steenkamp's death.
Gun at his bedside
The case against Pistorius is largely circumstantial, prosecutor Gerrie Nel said in his opening statement last week. Pistorius and Steenkamp were the only people in his house when he killed her.
Nel has been building a picture of what happened through the testimony of neighbors who heard screaming and bangs that night; experts; current and former friends of Pistorius; and a security guard who sped to the scene because of reports of gunshots.
Defense attorney Roux has gone after holes, doubts, discrepancies and inconsistencies in prosecution witness stories.
Many prosecution witnesses' accounts are consistent with Pistorius' version of events: that he got up in the night, went out to his balcony to get a fan, came back inside and heard noises in the bathroom that he thought came from an intruder.
He said he took the gun and fired while calling for Steenkamp to call police. When she didn't answer, he realized it could have been her in the bathroom, he said.
Former girlfriend testifies
Samantha Taylor, a former girlfriend of Pistorius, testified Friday that he reacted similarly once when she was sleeping at his house.
She said he once heard something hit a bathroom window and woke her up to ask if she'd heard it, too, before taking his gun and going to investigate. Taylor said Pistorius woke her up other times when he thought he'd heard a noise.
She also testified that Pistorius slept with a pistol on his bedside table or on the floor beside his prosthetic legs.
Prosecutors appear to have been trying to demonstrate that Pistorius and Steenkamp had a loud argument before the shooting, suggesting it's the reason he killed her.
Who was screaming?
Neighbors said they heard a woman screaming before the shots were fired. But the defense is proposing that what neighbors thought was Steenkamp screaming in fear for her life was in fact Pistorius when he realized what he had done.
Pistorius and at least two neighbors made phone calls to security after the shooting, allowing the defense to use phone records to establish a timeline of events.
One prosecution witness, the pathologist who conducted the autopsy on Steenkamp, cast doubt on the defense timeline by saying she had probably eaten about two hours before she died. Pistorius says the couple had gone to bed hours before that.
Judge Thokozile Masipa will decide the verdict. South Africa does not have jury trials.
In South Africa, premeditated murder carries a mandatory life sentence with a minimum of 25 years. Pistorius also could get five years for each gun indictment and 15 years for a firearms charge he also faces.
If he isn't convicted of premeditated murder, the sprinter could face a lesser charge of culpable homicide, a crime based on negligence. The sentence for culpable homicide is at the judge's discretion. The trial is expected to take at least three weeks.
CNN's Richard Allen Green reported and wrote from Pretoria, Faith Karimi and Emily Smith wrote from Atlanta. Marie-Louise Gumuchian in London contributed to this report.