THE judge in Oscar Pistorius's trial has said he cannot be found guilty of murder but that he was negligent in the killing of girlfriend Reeva Steenkamp.

Judge Thokozile Masipa's comments raise the possibility that the double-amputee Olympic athlete will be convicted of culpable homicide.

Ms Masipa said she felt Pistorius, dubbed Blade Runner due to his prosthetic limbs, acted negligently when he fatally shot Ms Steenkamp.

The judge then stopped delivering her judgement and adjourned until today, when a formal verdict in the case that has riveted South Africa and the world is expected.

Although there was no formal verdict, she indicated Pistorius would not be convicted of premeditated murder or a lesser murder charge, but he could be convicted of culpable homicide, in other words a negligent killing.

That normally carries a five-year jail sentence in South Africa but it can be changed by a judge depending on the specific circumstances of the killing.

Ms Masipa said she felt Pistorius acted negligently when he fatally shot Ms Steenkamp through a toilet door in his home in the pre-dawn hours of Valentine's Day last year.

While the judge did not announce a verdict, she said the prosecution had not proven beyond a reasonable doubt that Pistorius committed premeditated murder. She also ruled out a lesser murder charge.

"I am of the view that the accused acted too hastily and with excessive force," Ms Masipa said of Pistorius's actions on the fatal night last year.

"There were other means available … to deal with threats to his life. All the accused had to do was pick up his cell-phone and ring security, or run to the balcony and call for help."

She acknowledged that many people in South Africa have experienced crime.

"Many have been victims of violent crime but have not resorted to sleeping with firearms under their pillows," she said. "The accused had reasonable time to think, reflect and conduct himself. "I'm not persuaded that a reasonable person with the same disability would have fired the four shots.

"The accused knew there was a person behind the toilet door. He chose to use a firearm.

"It is clear his conduct is negligent."

The world-famous athlete has acknowledged firing four shots through a toilet door in his home, hitting Ms Steenkamp in the head, arm and hip area and killing her.

He says he mistook her for an intruder. The prosecution alleges the athlete intentionally killed his girlfriend, a model and budding reality TV star, after an argument, heard by neighbours.

"Culpable homicide is a competent verdict," the judge said.

Ms Masipa said there were "just not enough facts" to support a finding of premeditated murder.

As the judge spoke, Pistorius, 27, wept quietly, his shoulders ­shaking as he sat on a wooden bench. Ms Masipa earlier told Pistorius, 27, he could remain seated on the bench while she read her verdict out and until she asked him to stand for the judgement.

She described Pistorius as a "very poor witness" who had lost his composure on the stand and was at times "evasive," but she said that did not mean he was guilty of murder.

Pistorius faced 25 years to life in prison if convicted of premeditated murder.

He also faced years in jail if found guilty of murder without pre-planning.

If Pistorius is convicted on any charge, sentencing is likely be postponed.