Forensic investigator Johannes Vermeulen, with a cricket bat in hand, demonstrates on a mock-up toilet and door details of how the door could have been broken down, during the trial of Oscar Pistorius in court during the second week of his trial in Pretoria, South Africa, Wednesday, March 12, 2014. Pistorius is charged with the shooting death of his girlfriend Reeva Steenkamp on Valentine's Day in 2013. At center back is prosecutor Gerrie Nel. (AP Photo/Alexander Joe, Pool)

PRETORIA, South Africa - Oscar Pistorius was probably on his stumps when he fatally shot his girlfriend through a toilet door, a forensic analyst said Wednesday at the double-amputee athlete's murder trial.

The matter of whether Pistorius was on his stumps is critical because it tests his assertions about what exactly happened on the night he killed Reeva Steenkamp in his bathroom on Feb. 14, 2013.

The athlete has said he fearfully approached the bathroom on his stumps and shot Steenkamp by mistake, thinking she was an intruder. According to his account, he then put on his prostheses and tried to kick down the locked toilet door, and battered it with a cricket bat to get to his girlfriend after realizing what he had done.

Testimony Wednesday focused on the angle from which Pistorius hit the toilet door with a cricket bat, which could determine whether he was on his stumps, or was wearing his prostheses.

Police Col. J.G. Vermeulen, a forensic analyst, said he believed Pistorius was on his stumps when he fired through the toilet door, based on the angle of the bullet marks in the door, which was on display in the courtroom.

However, Vermeulen said the bat was used to hit the door from a low position, and he knelt and swung Pistorius' cricket bat at the door to demonstrate his point.

"It's quite low down on the door," Vermeulen testified about one of the marks he said were made by the bat. He said it was "not the normal position that I would expect from a mark from a cricket bat."

He said marks on the door were consistent with Pistorius "being in a natural position without his prostheses."

Defence lawyer Barry Roux countered that Pistorius hit the door with a "bent back" and that the low marks were consistent with such a body position.

Vermeulen also said a steel plate in the main bathroom in Pistorius' home had been damaged by being hit with a "hard" object, or after the object fell against it. The steel plate was new evidence. A photo of the damaged plate was shown.

Prosecutors say Pistorius intentionally shot Steenkamp, a 29-year-old model after a fight.

Those prosecutors used Vermeulen to show what they say are more inconsistencies in Pistorius' version by erecting the door in court and, behind it, an exact replica of the cubicle in Pistorius' house. There was even a replica toilet.

The bullet-marked door also had what appeared to be white tags to indicate the bullet holes. Pistorius shot at Steenkamp four times through the door, hitting her in the hip, arm and head. One shot missed, the court has heard.

Led by questions from prosecutor Gerrie Nel, Vermeulen removed his blazer and walked down from the witness stand and over to the door to demonstrate to the judge how he believes the door was hit in the pre-dawn hours of Valentine's Day last year.

He said he was particularly interested in two specific marks on the door that he concluded were made by the bat.

With the use of court photos and by kneeling down in court, Vermeulen showed the low position that the person could have been in when striking the door with the bat.

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Associated Press writer Torchia reported from Johannesburg.

News from © The Associated Press, 2014