The witness overheard the “row” which is said to have come from the South African runner’s property at the exclusive Silver Lakes Golf Estate between 2am and 3am on Valentine’s Day, the prosecution said.
Shortly afterwards, Reeva Steenkamp, 29, lay bleeding to death in Pistorius’s bathroom.
She was hit by three bullets – one in the head, the hip and arm, Pretoria Magistrates’ Court heard.
One witness reported hearing a shot, followed 17 minutes later by more shots, lead detective Hilton Botha said. “One of our witnesses heard a fight, two people talking loudly at each other... from two in the morning to three.”
Pistorius has admitted shooting the model with a 9mm pistol pulled from under his bed, but claims he did so thinking she was a burglar or burglars, who were in the bathroom. He said he opened fire in the dark because he was too scared to turn a light on.
Realising his mistake, he broke the door down with a cricket bat and carried his girlfriend downstairs, he added.
Mr Botha said there was “no way” he believed Pistorius’s version of events and a witness told police Pistorius’s lights were on after hearing gunshots.
The double-amputee has said he shot through the door while on his stumps. But the court heard the bullets’ trajectory was through the top of the door and Mr Botha claims the bullets were fired down, suggesting Pistorius was wearing his prosthetic legs when the shots were discharged.
He said: “I believe he knew she was in the bathroom and he shot four shots through the door.”
The court also heard that two boxes of testosterone and needles were found in Pistorius’s bedroom. But his lawyer Barry Roux said the substance was actually a herbal remedy called Testocompasutium co-enzyme.
Details were released of a row Pistorius had with a man over a girl at Kyalami racetrack where the athlete allegedly threatened to “f*** up” the rival. It was also claimed he was involved in another shooting at a restaurant in Johannesburg in January and asked the gun owner to take responsibility for the accident.
Pistorius told officials he had been a victim of crime and received death threats, but yesterday the court heard there was no record of this.
Mr Botha said he wanted Pistorius charged additionally with a weapons violation after unlicensed .38 calibre ammunition was found at the house.
The athlete – who sobbed in court – made notes with a silver pen as the case progressed.
In an affidavit, Pistorius said he and Miss Steenkamp were in love and he thought she was in bed when he got up in the dark and blasted through the door.
Cross-examining Mr Botha, Mr Roux said a post-mortem examination showed Miss Steenkamp’s bladder was empty, which he said is consistent with her getting up at 3am to go to the toilet.
Mr Roux asked repeatedly why the police did not make simple checks – over the lighting and whether Pistorius had other phones after police said two seized iPhones were not used to call police or paramedics.
The lawyer said Pistorius phoned the housing complex manager for help at 3.19am then Netcare hospital a minute later.
Officers found the victim covered in towels and wearing white shorts and a black top.
The prosecution believe Pistorius, who won two gold medals and a silver at London’s 2012 Paralympic Games, is a flight risk and are opposing bail.
Despite him being a world-famous athlete, Mr Botha said he believed he could still go on the run, drawing laughs from the court.
The case was adjourned to today when a decision over bail might be made.