AFP/Pretoria

"Blade Runner" Oscar Pistorius appears in court on Thursday to face judgement over the killing of his model girlfriend, ending a six-month trial that turned the amputee's private life into a global spectacle.

The 27-year-old celebrity athlete faces life behind bars -- and notoriety that would eclipse his athletic achievements -- if found guilty of deliberately killing lover Reeva Steenkamp on Valentine's Day 2013.

Judge Thokozile Masipa's ruling, on charges of murder and three firearms offenses, will likely be laid out in two days of careful legal argument and then a final verdict, perhaps on Friday.

The high-drama, half-year trial has fed intense media interest worldwide, with live broadcasts veering into the realm of TV reality shows.

Nearly 40 witnesses testified, including Pistorius, who broke down, weeping and at times vomiting as he heard how the 29-year-old blonde's head "exploded" like a watermelon under the impact of his hollow-point bullet.

Prosecutors described him as an egotistical liar obsessed with guns, fast cars and beautiful women, who was not prepared to take responsibility for his actions.

The court heard transcripts of phone messages in which the pair argued, Steenkamp texting: "I'm scared of you sometimes, of how you snap at me."

Defence lawyers sought to explain there are "two Oscars" -- a world-class athlete and a highly vulnerable individual with a serious disability who acted out of fear, not anger, when he fired the fatal shots.

All the while his supportive sister and the implacable mother of the woman he killed looked on from the packed public gallery.

At its heart, the trial is simple.

Pistorius killed the law graduate when he fired four shots through a locked toilet door in his upmarket Pretoria home.

The double-amputee athlete doesn't deny this. The only question is why he did it.

He says he thought he was shooting at an intruder and that Steenkamp was safely in bed.

The prosecution says he killed her in a fit of rage after an argument.

The trial featured neighbours who testified to hearing female screams then gunshots, as well as defence experts who said this was impossible.

- The verdict

Judge Masipa will begin proceedings by evaluating the evidence of each of the witnesses in turn, all the while careful to evoke strong case law and limit cause for appeal.

She will then turn to her judgement.

Unlike trial of US football hero OJ Simpson trial, who was controversially acquitted by a jury, Masipa is assisted only by two assessors.

She may decide that Pistorius is innocent, or that the state has not done enough to prove its case, resulting in an acquittal.

But if she decides Pistorius deliberately murdered Steenkamp, he could face a life sentence, which in South Africa means 25 years in jail.

Masipa could also decide that Pistorius did not kill her intentionally, but did act recklessly, opening the door to a lesser charge of culpable homicide, which could still carry a prison term.

Any guilty verdict is unlikely to be end of the matter.

There will be more courtroom arguments before a sentence is handed down and, most likely, an appeal to a higher court.

Whatever happens, his glittering sporting career is likely to be over.

Once a poster boy for disabled sport, Pistorius has been stripped of lucrative endorsement deals by global brands and has withdrawn from all competition.