PRETORIA: "Blade Runner" Oscar Pistorius put on his artificial legs and walked across his bedroom before firing four shots through a locked bathroom door, killing his cowering girlfriend in cold blood, prosecutors said on Tuesday.

Reeva Steenkamp, a law graduate and model, died after being hit by three handgun rounds, prosecutor Gerrie Nel said.

Pistorius wept uncontrollably in court as Nel outlined details of a shooting that has gripped South Africa and the millions around the world who saw the double amputee's track glory as the ultimate tale of triumph over adversity.

Later, in an affidavit read out by defence lawyer Barry Roux, Pistorius said he had been "deeply in love" with Steenkamp and had no intention of killing her.

Having had previous death threats, Pistorius said he slept with a 9 mm pistol under his bed in his plush Pretoria home in the heart of a well-secured gated community.

He and Steenkamp went to sleep on Wednesday night - the eve of Valentine's day - shortly after 10 p.m., he said.

However, in the middle of the night in pitch darkness, he awoke and thought an intruder had climbed through the window of his bathroom, Pistorius said.

He climbed out of bed without putting on his prosthetic legs and went towards the closed bathroom door, not realising Steenkamp was behind it, he said. He then fired several shots into the door, before shouting to Steenkamp to call the police.

Realising she was not in bed, he grabbed a cricket bat to beat down the bathroom door, and found his girlfriend slumped on the floor.

"I am absolutely mortified at the death of my beloved Reeva," he said in the affidavit. As Roux read the statement, Pistorius was crying uncontrollably, to the point magistrate Desmond Nair had to halt proceedings for several minutes.

"You need to concentrate on what's going on," he told Pistorius.