"Blade Runner" Oscar Pistorius put on his artificial legs and walked across his bedroom before firing four handgun rounds into the 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 rounds, prosecutor Gerrie Nel said.

Pistorius wept uncontrollably in court as Nel outlined details of the shooting in the early hours of Thursday.

Steenkamp's funeral is to be held later on Tuesday.

Defence lawyer Barry Roux disputed the murder charge, saying the facts surrounding the shooting were unclear.

"All we really know is she locked herself behind the toilet door and she was shot," he told the packed Pretoria courtroom.

However, Nel, his counterpart at the bail hearing, painted a picture of premeditated killing - a crime that carries a life sentence in South Africa.

"If I arm myself, walk a distance and murder a person, that is premeditated," he said. "The door is closed. There is no doubt. I walk seven metres and I kill."

"The motive is 'I want to kill'. That's it," he added.

The arrest last week of the 26-year-old Olympic and Paralympic sprinter stunned millions across the world who held him up as a hero for triumphing over adversity to compete with able-bodied athletes at the highest level of sport.

Initial reports suggesting Pistorius may have mistaken her for an intruder - a version Pistorius told his sister immediately after the shooting, Nel said.