After a two-week break in the trial, Pistorius' lawyers on Monday called Johan Stander, the first person 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," Mr Stander said Pistorius told him over the phone.

Mr Stander described how when he arrived at Pistorius' upmarket Pretoria home he saw the athlete carrying Steenkamp, a 29-year-old model, down the stairs.

"He was screaming, he was crying, he was praying," Mr Stander said.

"The expression on his face, an expression of sorrow, an expression of pain, he's crying, he's praying," Mr Stander said. "It was as if he was torn apart."

Stander, who said he considered himself a friend of 27-year-old Pistorius, said the night was not something he would want to experience again.

Pistorius was "broken, desperate, pleading," he said. "How he begged God to keep her alive."

"I saw the truth that morning, I saw it and I feel it," he said.

Pistorius' 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.

He initially told the court 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, he changed his testimony to say he fired the four shots accidentally.

Prosecutor Gerrie Nel has accused the athlete of "tailoring" his evidence, calling his account of the killing "a lie".

Pistorius faces up to 25 years in prison if he is found guilty of premeditated murder.

He fired four bullets through a toilet door, killing Steenkamp, who was in the toilet inside the athlete's house in an upmarket housing complex.

Prosecutors have argued that the Valentine's Day shooting came after a row between the couple, who had been dating for about three months.

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, Pistorious 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 forced presiding judge Thokozile Masipa to halt the proceedings to allow Pistorius to compose himself.

AFP