PRETORIA, South Africa >> RETORIA, South Africa (AP) — What exactly was Oscar Pistorius doing in the moments before he fatally shot his girlfriend in his home?

Was he, as the double-amputee Olympian testified Friday, hobbling fearfully on his stumps with his pistol down a passageway from his bedroom toward the bathroom after hearing a possible intruder there? Or, as the chief prosecutor contended, was he instead angrily pursuing his girlfriend in the midst of an argument?

Contradicting himself at times, Pistorius sparred with the prosecutor over the differing accounts of what happened on the night he killed Reeva Steenkamp by firing four times through the closed door of a toilet cubicle. The star athlete, who says the shooting was an accident because he mistook her for a robber, faces 25 years to life in prison if convicted of premeditated murder.

“My whole being was fixated on this person that I thought was in the bathroom,” Pistorius said during the third day of his cross-examination.

He said that as he moved toward the bathroom, he screamed to his girlfriend to get down from their bed and call the police. After hearing a noise that made him think someone was opening the toilet door to attack him, Pistorius said he opened fire. Only afterward, he testified, did he realize that Steenkamp was not in the bedroom but in the toilet cubicle.

Prosecutor Gerrie Nel, however, said an argument between the couple was the “only reasonable explanation” for why Pistorius, 27, shot the 29-year-old model as she stood behind the toilet door some three meters (yards) away in the pre-dawn hours of Valentine’s Day last year.

Citing earlier expert testimony, Nel noted that the trajectory of the three bullets that hit the model in the hip, arm and head showed she was standing behind the door and facing it. Steenkamp wasn’t scared of anyone “other than you,” Nel said to the athlete.

Nel argued that the position of items in the bedroom also indicated Pistorius’ story was a fabrication. A duvet on the floor in police photos shows the couple were awake and arguing just before the shooting and not in bed as Pistorius has claimed, he said. Pistorius said it was one of many items apparently moved by police after the shooting.

He relentlessly attacked Pistorius’ account, asking the runner why he didn’t determine where Steenkamp was and make sure she was OK before firing, and why he approached what he thought was a danger zone in the dark if he felt vulnerable on his stumps.

Nel noted that throughout Pistorius’ version Steenkamp “never uttered a word.”

“It’s not probable. It’s not possible,” the prosecutor said, asking why Steenkamp never responded to Pistorius’ panicked shouts of an intruder when she was in the cubicle.

“I agree with Mr. Nel she would have been terrified,” Pistorius said, “but I don’t think she would have shouted out … In her mind I must have been retreating toward the bathroom.” Nel responded that gave Steenkamp even more reason to talk to Pistorius, who was meters away.

“She was standing behind the toilet door talking to you when you shot her,” Nel said at the end of the first week of the athlete’s testimony.

“That’s not true,” replied Pistorius.

The trial in a wood-lined courtroom in the South African city of Pretoria has been closely followed around the world, which once admired Pistorius as a man who persevered despite his disability and reached the pinnacle of his career when he was allowed to run in the London Olympics in 2012.

Now, instead of signing autographs in packed stadiums, the multiple Paralympic champion is a solitary figure in the witness box. He stumbled in some of his testimony Friday, prompting the prosecutor to pounce on what he called inconsistencies.

“I am tired. It’s not going to change,” Pistorius said.

“You’re trying to cover up for lies,” Nel said, “and I’m not convinced.”

Judge Thokozile Masipa then asked Pistorius if he was too tired to continue testifying, saying: “You can be at a disadvantage when you’re in that box.”

Pistorius kept going.

Later, Masipa tried to rein in the prosecutor, telling him: “Mind your language. We don’t call a witness a liar, not while he’s in the witness box.”

The prosecutor has seized on virtually every opportunity to challenge the star athlete’s credibility, asserting that he had a string of unlikely excuses for why he wasn’t to blame in the gun charges he faces on top of murder. In casting doubt on the Olympian’s honesty, Nel is pushing the prosecution’s argument that Pistorius is also lying that he killed Steenkamp by mistake.

On Friday, Nel argued that Pistorius lied about an incident years ago — when he says someone shot at him from another car on a highway — to build a backstory that he had a long-held fear of being attacked.

Pistorius said he saw a “muzzle flash” and heard “a banging noise” as a black Mercedes drove past him, and he turned off the highway and went to a restaurant parking lot and called someone to pick him up. Nel asked for the identity of the caller; Pistorius replied that he couldn’t remember.

Pistorius is not allowed to consult with his lawyers during the cross-examination, which resumes Monday.