Pistorius to start second week in witness box

The day will mark the start of the 27-year-old's second week in the witness stand in his defence against murder charges for Reeva Steenkamp's death on Valentines' Day last year.

Prosecutor Gerrie Nel's relentless questioning has drawn tears and angry replies from the world-famous double amputee sprinter, who insists he shot Steenkamp four times by accident through a locked bathroom door.

Jumping in a seemingly haphazard way from one event or piece of evidence to another, Nel finished his interrogation Friday with the dramatic accusation that Pistorius knew exactly what he was doing when he fired the lethal shots.

"You knew Reeva was behind the door and you shot at her!" he said, with athlete replying softly "It's not true, milady."

The prosecutor rubbished Pistorius's claim that he rushed to his bathroom in the dead of night after hearing a noise, then fired at the locked cubicle door thinking an intruder was coming out to attack him.

"Instinct would have made sure Reeva was safe. That was never your instinct: to make sure she was safe," Nel replied when Pistorius said he rushed towards danger "out of instinct".

He openly called the athlete's version "a lie".

Pistorius was evasive during the tough questioning, with memory lapses in key parts concerning incriminating details.

"I'm not looking for an excuse, if I don't remember it I don't remember it!" he said, breaking down during one exchange about the placement of objects in his bedroom.

He accuses police of moving things on the crime scene, whose positions in photos afterwards called into question his version of events on February 14, 2013.

Pistorius says he woke up in the early morning hours, brought in two fans from his balcony, then switched to self-defence mode after hearing the noise in the bathroom.

By his own account the athlete whispered to Steenkamp, a 29-year-old model and aspiring TV actress, to call the police, before shouting loud at the intruders to get out, rushing with his gun to the bathroom, and firing at the cubicle door.

The accused says the model never replied when he started shouting, and that she never screamed while he fired the shots, but that he couldn't hear because his ears were ringing.

Several neighbours testified to hearing a woman's terrified screams that night.

Steenkamp's older sister branded Pistorius a "disgusting liar" after attending some of his testimony in court with her mother.

"He is trying to convince the court that they were really close and that he cared for her. It's not true," said Simone Steenkamp, 48.

Attending the trial "almost destroyed me", she told Britain's The Mail on Sunday.

"He knew we were there but he almost lost his balance and fell over when he saw us.

"Then he sat in the dock, smirking. He killed my sister and yet he still seems to be enjoying his celebrity status.

"During the adjournments he marched around as if he was still a star while my mother and I just wanted to hide away," she added.

"I don't understand how anyone could commit that act - kill someone - and behave like that."

Pistorius will likely remain on the stand for another few days.

The defence will then call up to 17 witnesses, including ballistics experts.

The double amputee gained world-wide fame for running on two fibre optic blades at the Paralympics and 2012 London Games. His legs were amputated below the knee shortly after he was born without calf bones.

The shooting brought his career to an abrupt halt.