Oscar Pistorius' defence team has said claims by a neighbour that she heard Reeva Steenkamp scream after she had been shot multiple times will be thrown into doubt by expert evidence.
The claim came on an emotional day in court, where Pistorius was seen wiping his eyes with a hankerchief and the prosecution's key witness wept.
Sky's Alex Crawford, who was in court, said: "We saw for the first time a crack in the athlete's demeanour. He spent a lot of time taking notes, but this really broke him."
Oscar Pistorius shot dead his model girlfriend Reeva Steenkamp
Neighbour Michelle Burger, who says she heard Ms Steenkamp being killed by Pistorius, was grilled by the athlete's defence team on the second day of the trial.
She told the packed courtroom in South Africa's administrative capital Pretoria she heard a woman screaming after shots were fired in Pistorius' residence.
Pistorius chats with his legal team during a break
But Pistorius' lawyer Barry Roux said: "We will debate the sequence of the bullets. We will have experts state that there was serious brain damage after the shot to the head, that it would not have been possible for her to scream at all.
"With the head shot, she would have dropped down immediately."
Ms Burger replied: "As I said [on Monday], I heard her voice just after the last shot. It could have been that it was as the last shot was fired."
Prosecutor Gerrie Nel interjected to say it was the last of four shots that struck Ms Steenkamp's head.
Pistorius looks on from the dock as the case unfolds
Mr Roux opened Tuesday's questioning by saying he wanted to focus on two aspects of Ms Burger, her "credibility and reliability".
The defence lawyer has repeatedly attempted to establish that Ms Burger had already decided she did not believe Pistorius' account of the evening - that he believed there was an intruder in his home - when she gave evidence contradicting his story.
She is the prosecution's key witness, as her account of hearing a woman's screams suggest Pistorius would have known that it was his girlfriend rather than an intruder when he opened fire.
The world's media is watching the case closely
But the defence says the screams came from Pistorius, who was upset that he had killed Ms Steenkamp.
A tense exchange between Mr Roux and Ms Burger came to a climax when he said he had asked her the same question eight times.
"I'm going to be really slow this time," he said. "You heard at the bail application that it was put on behalf of Mr Pistorius that Reeva did not scream that night, is that correct?"
After giving an unclear answer, Judge Thokozile Masipa intervened and insisted that she had to make herself clear. Eventually, the witness admitted she had heard about Pistorius' claims.
Pistorius' family are in the public gallery
Mr Roux said: "You've watched Sky News, you've watched other channels, and you've got retrospective knowledge, and you take that knowledge and you come and give evidence today as if it's the knowledge of that fateful evening."
Ms Burger, who had been composed through two days of aggressive cross-examination, wept as she finished her testimony and broke down as she recalled the "raw emotion" she felt after the killing.
She said she often relives the "terrifying screams".
At around the same time, Pistorius was seen reaching for a hankerchief from his inside pocket and wiping his eyes.
The Pretoria home of Pistorius pictured after the shooting
Later, Ms Burger's husband Charl Peter Johnson took to the witness stand.
He said: "We were under the impression that they were being held up in their house.
"I lay in bed thinking of how I can improve the security around my house. I fell asleep at about 4am.
"I went to work early around 6am and I remembered surfing on the web for security gates for costs."
Pistorius turns to chat to his uncle
He said he too heard screams.
Earlier, the trial was temporarily delayed after an image of the witness was used by a South African news organisation.
The trial is being televised, but witnesses can choose not to appear on camera.
Ms Burger did not want to be filmed or pictured, and the case was temporarily adjourned in the morning after Judge Masipa was alerted. She said she viewed the error as "serious" and ordered an investigation.
The Paralympic athlete looks down at his notes
Pistorius, a double-amputee, is accused of the premeditated murder of Ms Steenkamp last Valentine's Day after a jealous row.
He is also accused of the illegal possession of ammunition and two additional counts relating to shooting a gun in public in two separate incidents before the killing.
The 27-year-old, who is known as the Blade Runner, denies all the charges and claims he shot his girlfriend after mistaking her for an intruder.
The trial, large parts of which can be broadcast live after a landmark ruling, is scheduled to last for three weeks and will hear from more than 100 witnesses.
South Africa does not have a jury system. Instead, Judge Masipa will decide his fate.
If Pistorius is found guilty he could be jailed for at least 25 years.
:: Sky News is broadcasting live coverage of the trial, and a special highlights programme will be broadcast every weekday at 9.30pm.
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