After a two-week break in the trial, the defence called Johan Stander, the first man to arrive at the crime scene after the Paralympic gold medallist shot his girlfriend Reeva Steenkamp on Valentine's Day last year.
"Oom (Afrikaans for uncle) Johan, please, please, please come to my house, I shot Reeva," Stander says Pistorius told him over the phone.
When he arrived at Pistorius's upmarket Pretoria home, Stander described seeing the athlete carrying Steenkamp, a 29-year-old model and law graduate, down the stairs.
"He was screaming, he was crying, he was praying," said Stander, a man with grey hair and glasses who spoke in a hoarse voice.
"The expression on his face, an expression of sorrow, an expression of pain, he's crying, he's praying," said Stander. "It was as if he was torn apart."
Stander, who said he considered himself a friend of the 27-year-old Pistorius, said the night was not something he would want to experience again.
Pistorius was "broken, desperate, pleading," said Stander. "How he begged God to keep her alive."
"I saw the truth that morning, I saw it and I feel it," he said.
Defence on the attack
Pistorius's lawyers will spend at least the next two weeks trying to firm up the athlete's account of the killing and counter the state's claim he shot his girlfriend after an argument.
Under days of ferocious cross-examination last month, Pistorius appeared to change his defence, casting doubt on his credibility.
The runner initially told the court that he shot Steenkamp through a locked toilet door, thinking she was an intruder coming to attack him in the dead of night.
But buckling under pressure, the Paralympian -- who soared to international fame as the first double-amputee to run against able-bodied athletes at the 2012 London Olympics - changed his testimony to say he fired the four shots accidentally.
State prosecutor Gerrie Nel has accused the athlete of "tailoring" his evidence, calling his account of the killing "a lie".
Beginning his cross-examination of Stander, Nel asked him if Pistorius ever said to him that he had fired accidentally.
"He never said I accidentally shot her," said Nel. "He said... thought she was an intruder."
Defence lawyer Barry Roux later called Stander's daughter Carice Viljoen, who said she heard a man calling for help in the dead of the night, apparently supporting the defence version of events that it wasn't Steenkamp screaming, but Pistorius.
"I could hear a man shouting, meaning there must be terrible trouble...," she said.
Pistorius, nicknamed the "Blade Runner," faces up to 25 years in prison if he is found guilty of premeditated murder.
He fired four bullets through a lavatory door, killing Steenkamp who was in the cubicle inside the athlete's house in an upmarket housing complex in the capital Pretoria.
Prosecutors have argued that the Valentine's Day shooting came after a row between the couple who had been dating for around three months.
The trial was adjourned until Tuesday after Roux said he had no more witnesses to call on Monday.
Proceedings will also break on Wednesday, which has been declared a public holiday for South Africa's general election, before resuming on Thursday.
Among the witnesses expected to give evidence this week is a psychologist who will speak to the athlete's physical vulnerability, after details emerged in court of his obsession with guns.
At times, the world famous sprinter has wept and retched in court, in a trial that is being broadcast live on television.
His emotional outbursts, including loud wailing and sobbing on several occasions, have forced presiding Judge Thokozile Masipa to halt the proceedings several times to allow Pistorius to compose himself.