PRETORIA, South Africa — Kneeling in court and swinging a cricket bat at Oscar Pistorius’ toilet door, a South African forensic analyst demonstrated today how the double-amputee athlete may have bashed the door to get to the girlfriend he had just fatally shot.

Col. J.G. Vermeulen said he believed Pistorius was on his stumps when he swung his bat at the brown cubicle door.

The defense, on cross-examination of the policeman, insisted instead that Pistorius was wearing his prosthetic legs when hitting the door in the pre-dawn hours of Valentine’s Day last year — and the marks from the bat on the door were lower down because the athlete swung with a bent back.

The intricate argument over whether Pistorius, the first amputee to run at the Olympics and now on trial for murder, was on his prosthetic limbs or not is important because it could match parts of his story that he accidentally shot Reeva Steenkamp. It could also show that he is lying.

The athlete has said he fearfully approached the bathroom on his stumps on Feb. 14 last year and shot Steenkamp by mistake, thinking she was an intruder hiding behind the door. 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.

Prosecutors maintain he intentionally shot the 29-year-old model and have charged him with murder. He pleaded not guilty to all charges against him, which also include three firearm related counts.