Police Col. J.G. Vermeulen testified about the bullet-marked door, a critical piece of evidence in the case against the double-amputee Olympian, who fired through the door on Feb. 14, 2013, killing girlfriend Reeva Steenkamp.
Defense lawyer Barry Roux raised questions about possible contamination of evidence related to police handling of the door. Roux also suggested Vermeulen did not consider Pistorius' version of events, despite the colonel's assertion that he acted objectively in his investigation.
Roux indicated that police investigators might have also left a shoe print on the door, the door itself might have been kept in a policeman's office and not in proper evidence storage, and missing fragments from the door weren't examined.
Earlier, Vermeulen knelt in court and swung a cricket bat at Pistorius' toilet door, demonstrating how the double-amputee athlete may have bashed the door to get to the girlfriend he had just fatally shot.
Vermeulen said he believed Pistorius was on his stumps when he swung his bat at the cubicle door.
The defense 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 Steenkamp. Or it could also suggest that he is lying.
Last year, prosecutors maintained that Pistorius was on his prosthetic limbs when he fired through the door, but in a reversal of that position, prosecutor Gerrie Nel said in court Wednesday that he did not dispute the defense's contention that the runner was indeed on his stumps at the time.
The earlier, mistaken claim by prosecutors was used by them to argue there was premeditation in the killing because they believed the disabled runner planned the killing while putting his prosthetics limbs on.
The 27-year-old athlete has said he fearfully approached the bathroom on his stumps 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.
The actual door that Pistorius shot through a year ago was erected in the Pretoria courtroom Wednesday. The bat he used that night was also used in the demonstrations. And there was even a toilet cubicle behind the door, recreated to the exact specifications of the small area of Pistorius' bathroom where Steenkamp was fatally shot, Vermeulen said. It included a toilet bowl.
The door also had what appeared to be white tags on it and, below the handle, four bullet holes were clearly visible. Steenkamp was hit three times in the hip, arm and head. One shot missed, the court has heard.
Earlier, Vermeulen also said a metal panel on the wall of the main bathroom in Pistorius' home had been damaged by being hit with a "hard" object, or after the object fell against it. The panel was new evidence. A photo of the damaged plate was shown.
Pistorius faces a possible life sentence if convicted of murder for killing Steenkamp. The judge, who watched the demonstrations Wednesday, will ultimately decide on the verdict. There is no trial by jury in South Africa.
Associated Press writer Torchia reported from Johannesburg.