The first witness in the Oscar Pistorius murder trial testified Monday to hearing "blood-curdling" screams before the sound of four gunshots on the night the double-amputee Olympian killed his girlfriend.

The high-profile trial concluded its first day with Michell Burger, a woman who lives on an estate next to Pistorius's gated community, defending her memory of what happened in the pre-dawn hours of Feb. 14 last year, when Pistorius killed Reeva Steenkamp by shooting four times through a door in his bathroom.

reeva-steenkamp-cp-04001060

Oscar Pistorius is accused of murder in the Valentine's Day shooting of his girlfriend, Reeva Steenkamp. (Stimulii/Associated Press)

Pistorius has pleaded not guilty in the case. He says he killed Steenkamp by mistake thinking she was a dangerous intruder in his house, but prosecutors believe the world-famous athlete shot his girlfriend after a fight and immediately tried to paint a picture of a loud argument before the fatal shots by using Burger's testimony.

"It was very traumatic," Burger said, speaking in Afrikaans through an interpreter and in answer to questions from lead prosecutor Gerrie Nel.

"You could hear it was blood-curdling screams. You can't translate it into words. The anxiousness in her voice, and fear. It leaves you cold."

Burger said: "She screamed terribly and she yelled for help" and testified that after the gunshots a man shouted for help.

Pistorius, who also pleaded not guilty to three other counts relating to shooting guns in public and illegal possession of ammunition, wore a dark grey suit and black tie. The star sprinter spent the first 30 minutes of the trial standing, before his defence lawyer, Barry Roux, asked the judge for permission for Pistorius to sit.

Roux, Pistorius's lawyer, opened his cross-examination by asking Burger if she thought Pistorius was a liar. She didn't directly answer that with a yes or no, but repeated her recollection of the night's events.

"I can only tell the court what I heard that evening," Burger said. "I cannot understand how I could clearly hear a woman scream but Mr. Pistorius could not hear it."

But Roux argued she had changed her testimony from the written statement she gave to police soon after the shooting, only adding "blood-curdling" as a description of the screams in court.

Burger's testimony contradicts Pistorius's version of events, because he said he thought Steenkamp was in bed and he did not describe any woman screaming.

Pistorius lawyer takes aim at inconsistencies in state's case

Defence lawyer Kenny Oldwadge laid out Pistorius's legal strategy, reading a statement from the runner in which he says the killing was an accident and that there were inconsistencies in the state's case, as well as an attempt to introduce inadmissible character evidence to discredit him.

Steenkamp family in court

Reeva Steenkamp’s mother, June, was in court on Monday.

"I want to look at Oscar, really look him in the eyes, and see for myself the truth about what he did to Reeva," she said in an interview published by the Pretoria News.

"Whatever the court decides at the end of his trial, I will be ready to forgive him ... But first I want to force him to look at me, Reeva's mother, and see the pain and anguish he has inflicted on me. I feel I need that,"

When he entered court, Pistorius walked past Steenkamp, but didn’t say anything.

At the time of her death, Reeva Steenkamp, 29, was a glamorous model and budding reality TV show star. 

In the statement, Pistorius said he brought two fans in from the balcony on the night of the killing, after speaking to his girlfriend who was in bed beside him. He said Steenkamp must have gone into the bathroom while he was fetching the fans. Pistorius said he did not notice that she had gone and heard the bathroom window open.

"I approached the bathroom, armed with my firearm, so as to defend Reeva and I," Pistorius said in the statement that was read by his lawyer.

He said he then heard a noise in the toilet, and was in a "fearful state" because he was unable to run away or defend himself physically since he was not wearing his prostheses.

"The state has embarked on a strategy to rely on unsubstantiated allegations," he said, citing a neighbour's testimony that an argument had been heard in his home.

According to Pistorius's statement, other neighbours living nearby said they had not heard any argument.

He also cited evidence provided by police detective Hilton Botha as "false in material respects."

"The scene was contaminated, disturbed and tampered with," the defence statement said. "This feature of the state's case will be dealt with when Botha, among others, gives evidence."

Televised trial full of drama

Parts of the trial will be broadcast on live television, both in South Africa and across the world. A South African cable channel has been launched which will provide 24-hour coverage of the Pistorius trial, using commentators and prepared feature stories when the court is not in session.

Ouside the courthouse, a drone carrying cameras flew over the entrance in grey, drizzly skies. Several broadcasters massed live broadcast satellite trucks around the courthouse.

If convicted on the murder charge, Pistorius could be sent to prison for at least 25 years before the chance of parole, the minimum time someone must serve if given a life sentence in South Africa. South Africa does not have the death penalty.

A lesser sentence is possible if Pistorius is found guilty of murder but without premeditation. He also could be convicted of culpable homicide, South Africa's version of manslaughter in which someone is killed through negligence.

The additional firearms charges relate to him allegedly shooting out of the sunroof of a car in one incident and another when he allegedly fired a gun inside a restaurant, apparently by mistake.

Judge Thokozile Masipa, hearing the biggest trial of her career, will decide if Pistorius is guilty of murder. South Africa has no trial by jury.

The trial is set to resume Tuesday morning at 3 a.m. ET.