Double amputee Oscar Pistorius was standing on his stumps when he smashed down a locked toilet door to reach his shot girlfriend, a South African police forensic expert said. (Reuters)

A door looms large in the trial of Oscar Pistorius and today it made its appearance.

Standing before its bullet-riddled facade and hefting a cricket bat, a forensic scientist reconstructed how Pistorius may have bashed open the door just after shooting dead his girlfriend. Blemishes marking the door appear to confirm Pistorius was on his stumps when he broke down the door, the forensic scientist testified. If true, it would confirm a key aspect of Pistorius’s story that he hadn’t been wearing his prosthetic limbs when he killed his girlfriend.

Despite its entry, and the questions it raises, the trial still hinges on the moments right before Pistorius knocked open his bathroom door. Did Pistorius think his girlfriend, Reeva Steenkamp, had actually been an intruder when he shot and killed her on Valentine’s Day in 2013?

Pistorius, a South African Olympian despite the fact he doesn’t have legs, claims he woke in the middle of the night and hobbled to the bathroom without his prosthetic legs. There, he says, he thought he’d discovered an intruder lurking inside and shot through the door.

Prosecutors, however, allege he and Steenkamp had had a vicious argument that culminated in Steenkamp’s murder.

Now, two days after Pistorius vomited while hearing the graphic description of the trauma he inflicted on his girlfriend, the bathroom door, removed immediately after the killing, has resurfaced. It represents a crucial bit of evidence, and legal experts expect it may finally illuminate what actually occurred the night of Steenkamp’s killing.

Throughout the trial, a troubling image of Pistorius has emerged — and witnesses and experts have repeatedly challenged his version of events. Friend Darren Fresco described the Olympian as having “a big love” for guns. Fresco testified he’d witnessed the athlete fire guns in public two separate occasions in the six months before Steenkamp’s death.

It first happened, he said, when Pistorius had suddenly fired his gun through the sunroof of a moving car in September 2012. Then again in January 2013 when the runner fired his weapon by accident under a table at a crowded Johannesburg restaurant.

Pistorius’ timeline of events has also come into question. One expert, a pathologist, says Steenkamp’s autopsy proved she had eaten within two hours of her shooting — contradicting Pistorius’ recollection that the two had gone to bed around 10 a.m., six hours before she was killed.

Also, four separate witnesses have testified they heard a woman screaming that night — and believed it had been Steenkamp’s voice. Pistorius claims it was he who had screamed.

If found guilty of murder, Pistorius faces 25 years in prison.