A witness in the Oscar Pistorius trial has described hearing "blood-curdling screams" on the night the Paralympian shot his girlfriend dead.
Michell Burger, who lived on the neighbouring estate to the Silverwoods Estate in Pretoria where Pistorius lived, described hearing a woman screaming followed by four gunshots on the night of model Reeva Steenkamp's death.
Her evidence came on the first day of Pistorius's highly anticipated trial at the North Gauteng High Court in Pretoria on Monday, where the six-time Paralympic Games gold medal winner formally pleaded not guilty to four charges including the murder of Miss Steenkamp.
Prosecutors allege the 27-year-old shot model and reality TV star Miss Steenkamp, 29, through the bathroom door of his home.
Ms Burger, a neighbour of Pistorius who lives in the Silver Stream Estate, described waking up at around 3am to a woman's "terrible screams".
Speaking through an interpreter, she said: "We woke up from the screams. My husband jumped up and went to the balcony."
Ms Burger told the court it had been traumatic to hear the "blood-curdling screams", adding: "It leaves you cold."
She said she also heard a man screaming for help, adding: "Three times he yelled for help."
Ms Burger said she and her husband called security at their estate to report the screams and what they thought was a break-in.
She added: "I heard her screams again, it was worse, it was more intense. Just after her screams, I heard four shots, it was four gunshots that I heard."
Asked to describe the successive shots, she said there was a pause between the first and second which was longer between the second and third shots and the third and fourth.
She said: "I told my husband that I do not hope that that woman saw her husband being shot in front of her because after he screamed for help we didn't hear him again."
The start of the trial - which is being watched by the world - was delayed by an hour and a half on Monday as the court waited for Afrikaans interpreters.
As it got under way, Judge Thokozile Masipa, who will come to a decision at the end of the trial, and assessors Janet Henzen-Du Toit and Themba Mazibuko, heard Pistorius formally deny the murder of Ms Steenkamp.
The double amputee is charged with the murder of Ms Steenkamp, whom he shot dead at his home on Valentine's Day last year.
He also faces charges under the Firearms Control Act, relating to firing a gun through the sunroof of a car in September 2012, and firing a gun whilst in a restaurant in Johannesburg in January last year, as well as possession of ammunition.
Pistorius was asked by Judge Masipa if he understood the charge of murdering Ms Steenkamp, to which he replied: "I do, I do, my lady."
Asked how he pleaded, he said: "Not guilty, my lady."
The Paralympic star, wearing a dark suit, white shirt and dark tie, entered not guilty pleas to four charges in the packed courtroom in Pretoria.
The opening moments of his trial were televised in a first for South Africa.
Pistorius, dubbed the "Blade Runner" for his prosthetic legs, admits shooting Miss Steenkamp dead at his home but claims he thought she was an intruder.
His trial is expected to hear from more than 100 witnesses, including neighbours who claim to have heard screams from his house that night, as well as former girlfriends of the athlete.
In court on Monday, Pistorius, who was supported by family members including siblings Carl and Aimee and his uncle Arnold, came face to face with Miss Steenkamp's mother June, who is attending the trial.
Prosecutor Gerrie Nel told the court: "They were the only two people in the house. There were no eyewitnesses.
"The state's case is based on circumstantial evidence."
He said evidence included what neighbours heard, and prosecutors would argue that "a certain inference" could be drawn from the scene.
"We argue that the accused's version in the bail application and today could not reasonably possibly be true, should be rejected," he said, adding: "The only inference from the circumstantial evidence would be that the accused shot and killed the deceased."
The court was read a statement from Pistorius in which he claimed he mistakenly thought there was an intruder in his home, leading him to open fire in an attempt to protect himself and Miss Steenkamp.
The statement, read by Pistorius's defence lawyer while the athlete remained standing, said the scene had been contaminated and disturbed.
In it, the Paralympian said he did not intend to kill his then-girlfriend that night and they had not argued that night.
He said: "I deny this allegation in the strongest terms because there was no argument. The allegation that I wanted to shoot (or kill) Reeva cannot be further from the truth."
The mandatory sentence for premeditated murder in South Africa is life with a minimum of 25 years in prison, meaning that if Pistorius is found guilty, he will be over 50 when he is released.
Under cross-examination, Ms Burger told the court: "I could not understand how I could clearly hear a woman scream but Mr Pistorius couldn't hear that. I couldn't understand that.
"I agree that I heard four gunshots and that I heard a man screaming for help three times," she said, describing the screams as "fear-stricken" and "petrified".
She added: "I couldn't understand why Mr Pistorius didn't hear the screams of the woman and if he didn't hear the screams of the woman that's a question that needs to be asked to Mr Pistorius."
Ms Burger told the court that, while she had clearly heard four gunshots, her husband had heard "four, five or six" shots.
She said the evening was confusing but also "distressing", telling the court: "The events of that evening was extremely traumatic for me. The fear in that woman's voice is difficult to explain to the court."
She said she was traumatised by what she had heard: "It was a very emotional situation to have to hear. The absolute petrified screams and shouts, it was not just another evening, it was extremely emotional."
At one point, the witness offered to speak in English as she said some of her words were not being translated correctly from Afrikaans to English by the interpreter.
Asked to explain when the screams were in relation to the gunshots, she said: "I heard her screaming first, then I heard her call for help. Then I heard a man call for help three times.
"I then made a call, I gave the phone to my husband and he spoke to security. Afterwards I heard the woman's petrified screams again."
She added: "I heard her screaming sometime during the shots", and said the last time she heard her shout was just after the shots.
Describing the traumatic experience of what she heard that night, she said: "I was convinced that that woman was being attacked, she and her husband were being attacked in their house. I was convinced it was an attack in the house by robbers. There was no doubt in my mind, because of the fear in that woman's voice."
She added: "Because of the climax of her shouts I knew something terrible was happening in that house.
"You only shout like that if your life is really threatened."
Under questioning from defence lawyer Barry Roux, Ms Burger said she definitely heard gunshots, but did not hear the sound of a cricket bat being used to hit the door.
The case in Pretoria was adjourned until Tuesday morning at 9.30am local time (7.30am GMT).