Prosecutors accused Oscar Pistorius on Friday of tailoring evidence and overplaying his deep fear of crime to justify shooting dead his girlfriend Reeva Steenkamp.

During a third day of stern cross-examination, prosecutor Gerrie Nel insisted that the 27-year-old South African athlete was selective in his recollection of events.

Amid questioning on the minutiae of what happened that Valentine’s Day night and over apparent discrepancies in Pistorius’s accounts, the sprinter grew increasingly agitated.

“I’m not looking for an excuse, if I don’t remember it I don’t remember it,” he said, breaking down into tears during one exchange about the placement of objects in his bedroom.

“This is the night I lost the person I most cared about, I don’t know how people don’t understand that,” he said.

Nel had accused him earlier of changing his version of events and of not remembering details that could be detrimental to the athlete’s case. “Why are you changing your evidence?” Nel asked.

“I’m tired, my lady,” Pistorius told the judge directly.

“I’m not convinced about your answer now, I think you’re trying to cover up for lies,” Nel replied.

Nel also tried to show Pistorius was not as concerned about crime as he claimed because he did not quickly fix a broken window and may not have turned on his house alarm the night that the Steenkamp was killed.

“Did you ever go into a police station and complain about anything?” asked Nel, after Pistorius listed the times he had been a victim of crime.

“No, I did not,” Pistorius said, “except for the police stealing my watches, my lady,” he said referring to luxury timepieces that had gone missing at the Steenkamp crime scene.

The athlete said he fired his gun through his locked bathroom door thinking the 29-year-old model and aspiring actor was an intruder, because he had a heightened fear of crime.

Before starting a third day of cross-examination, Nel said Steenkamp’s mother, June, acknowledged Pistorius had requested a family meeting.

Nel had attacked Pistorius for his public apology to the Steenkamps when he took the stand on Monday, but the double amputee sprinter said he had once asked to meet his girlfriend’s family in person, presumably to apologise.

June Steenkamp’s lawyer confirmed the request, Nel told the court.

“But they weren’t ready. Mrs Steenkamp felt it was important to be put on the record,” he said.

June Steenkamp has been hard on Pistorius and was quoted in a newspaper this week saying that the athlete had gone from “hero to devil” after killing her daughter.

“My presence unnerves him, I’m sure of it. He’s answerable to me,” Steenkamp told Britain’s Daily Mirror.

Friday marked a difficult week on the stand for Pistorius, having been accused of lying and fabricating evidence.

“Your version is so improbable that nobody would ever think it’s reasonably, possibly true – it’s so impossible,” Nel said during the cross-examination. “Your version … is a lie.”

Confronted with crime scene pictures, Pistorius said police had tampered with objects when they arrived at his house. Someone moved fans, pulled the duvet on to the floor and opened the curtains, he said.

“Is this one big conspiracy?” asked Nel. “They would do all this to you?”

Pistorius has been charged with murdering Steenkamp in the early morning hours of 14 February 2013. He faces a life sentence if convicted.

He has said he fired the shots accidentally and did not mean to kill anyone. He also testified that he feared someone was coming through the toilet door and that his life was in danger.

The account was questioned at length by Nel, who drew a concession from Pistorius that the shots should not have been fired at all.

“We know for a fact there were no intruders in your house that night, we know for a fact there was no ladder against the wall,” Nel said. “We know for a fact that you had no reason to shoot, objectively speaking.”

Pistorius told the judge: “That’s correct, my lady.”

Pistorius’s cross-examination is a key point in his trial and a stern test of both his version of events and of his resolve.

Defence lawyer Barry Roux is expected to call up to 17 witnesses in the remainder of the case.

Scheduled to run for three weeks, the trial has been extended until mid-May although it could go on longer.