Pistorius, a double amputee, is accused of murdering girlfriend Reeva Steenkamp on Valentine's Day last year. He maintains he shot her through a locked toilet door believing an intruder was lurking in his luxury Pretoria home.
His friend, Darren Fresco, told the court in Pretoria that he had been driving south of Johannesburg in September 2012 when Pistorius, nicknamed "Bladerunner" for his carbon fibre prosthetics, and his then girlfriend Samantha Taylor were flagged down.
"Another officer went over to the passenger seat where Oscar Pistorius was sitting and he picked up a gun. There was a verbal altercation between the accused and the officer," Fresco said.
"Pistorius said to the officer, 'You can't just touch another man's gun,'" Fresco said. "Then they argued."
After being allowed to leave, Pistorius "out of the blue" fired the gun through the open sunroof of the car, to the astonishment of Fresco, who was driving at the time.
"Apologies for my language, but I asked him if he was f***ing mad," Fresco told the court. "He just laughed."
"Being a friend I said I would, with pleasure," the long-haired Fresco said.
Pistorius is facing separate gun charges for the two incidents, part of the prosecution's attempts to paint Pistorius as a cocky, gun-obsessed hot-head who does not like to take responsibility for his actions.
Of the four rounds he fired through the toilet door, three hit his girlfriend, a 29-year-old model and law graduate, on the hip, shoulder and head.
Earlier, state pathologist Gert Saayman had told the court that food found in Steenkamp's stomach suggested she had eaten food at about 1 a.m. - two hours before she died and in contradiction to Pistorius' testimony that the couple went to bed at 10 p.m.
Saayman said Steenkamp would have most certainly screamed after being shot in the arm and hip before a final shot in the head killed her.
"After the first shot on the hip, screaming would have been possible, and expression of fear or anguish," Saayman said. "It would be abnormal for someone not to scream."
Some of Pistorius' neighbours said in their court testimonies last week they heard a woman screaming during the shooting, but Pistorius' lawyer insists what they heard were high-pitched cries from his client.
If found guilty of murder, Pistorius faces at least 25 years behind bars.
The killing has ignited debate about gun control and domestic violence in South Africa, where many women die at the hands of relatives.
- Crime & Justice
- Society & Culture
- Oscar Pistorius
- Reeva Steenkamp