PRETORIA, South Africa (AP) — Oscar Pistorius told a packed courtroom Tuesday that he shot his girlfriend to death by mistake, thinking she was a robber. The prosecutor called it premeditated murder.

The double amputee said in an affidavit read by his lawyer at his bail hearing that he felt vulnerable because he did not have on his prosthetic legs when he pumped bullets into the locked bathroom door.

Then, Pistorius said in the sworn statement, he realised that model Reeva Steenkamp was not in his bed.

"It filled me with horror and fear," he said.

He put on his prosthetic legs, tried to kick down the door, then bashed it in with a cricket bat to find Steenkamp, 29, shot inside. He said he ran downstairs with her, but "She died in my arms."

Prosecutor Gerrie Nel on Tuesday charged the 26-year-old athlete and Olympian with premeditated murder, alleging he took the time to put on his legs and walk some seven metres from the bed to the bathroom door before opening fire. A conviction of premeditated murder carries a mandatory sentence of life in jail.

The Valentine's Day shooting death has shocked South Africans and many around the world who idolised Pistorius for overcoming adversity to become a sports champion, competing in the London Olympics last year in track besides being a Paralympian.

Steenkamp was a model and law graduate who made her debut on a South African reality TV programme that was broadcast on Saturday, two days after her death.

The magistrate ruled that Pistorius faces the harshest bail requirements available in South African law.

Nel told the court that Pistorius fired into the door of a small bathroom where Steenkamp was cowering after a shouting match. He fired four times and three bullets hit Steenkamp, the prosecutor said.

"She couldn't go anywhere. You can run nowhere," prosecutor Nel argued. "It must have been horrific."

Pistorius sobbed softly as his lawyer, Barry Roux, insisted the shooting was an accident and that there was no evidence to substantiate a murder charge.

"Was it to kill her, or was it to get her out?" he asked about the broken-down door. "We submit it is not even murder. There is no concession this is a murder."

He said the state had provided no evidence that the couple quarrelled nor offered a motive.

Nel rebutted: "The motive is `I want to kill.'"

Pistorius was born without fibula bones and had his legs amputated when he was 11 months.

The man known as the Blade Runner because of his running prostheses has lost several valuable sponsorships estimated to be worth more than $1 million a year.