Warrant officer Hilton Botha, a detective with 24 years on the force, also told the city's magistrates court in a bail hearing yesterday that police had found two containers of testosterone and needles in Pistorius's bedroom. The athlete's defence team disputed the claim.
Pistorius – a double amputee dubbed Blade Runner because of his carbon fibre racing blades –sobbed uncontrollably as Mr Botha presented his testimony about the death of Reeva Steenkamp, 29.
The law graduate and model was in the toilet of the athlete's home when she was shot dead in the early hours of February 14 –Valentine's Day. She had been hit in the head, arm and hip.
Mr Botha told the court: "One of our witnesses heard a fight, two people talking loudly at each other ... from two in the morning to three."
The detective, who arrived on the scene an hour after the shooting, challenged the version of event given by Pistorius in an affidavit earlier this week, in which the athlete said he believed he was shooting at an intruder.
Mr Botha said: "I believe he knew she was in the bathroom and he fired four shots through the door."
He added the angle at which the rounds were fired suggested they were aimed at somebody on the toilet.
Pistorius had said he moved into the bathroom on his stumps – the reason he felt so vulnerable – but Mr Botha said the shots went in a "top to bottom" trajectory, suggesting Pistorius was wearing his artificial legs when he pulled the trigger.
"It seems to me it was fired down," he said.
One of the spent rounds was recovered from the toilet bowl, Mr Botha said.
He also cited a witness on the upmarket gated community near Pretoria where Pistorius lived as saying he heard a shot, followed 17 minutes later by more shots.
Another witness spoke of a shot, followed by screams, followed by more shots, he said.
Mr Botha said he wanted Pistorius charged additionally with a weapons violation because unlicensed .38 calibre ammunition was found at the house.
The athlete – who was again sobbing in court – made notes with a silver pen as the case progressed.
He told officials he had been a victim of crime and received death threats, but the court heard there were no records of this.
After vigorous questioning from the defence team, Mr Botha estimated the distance between the witnesses and Pistorius's home to be at 300 metres.
Lead defence counsel Barry Roux also disputed Mr Botha's reference to testosterone, saying the substance was a legitimate herbal remedy called testo-composutim co-enzyme.
Administering testosterone as an anabolic agent is banned at all times under World Anti-Doping Agency rules for sports people.
The court heard two mobile phones were seized at the property and neither had been used to call the police or paramedics.
Mr Roux said a post-mortem examination showed Miss Steenkamp's bladder was empty which he said was 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 four hours of testimony, the bail hearing was adjourned until today.
The hearing is expected to conclude this week, after the defence and prosecution have outlined their central arguments. It may then be several months before a trial.
If convicted of premeditated murder, Pistorius faces a life sentence in prison.