Prosecutors, however, said the double-amputee Olympian committed premeditated murder, planning the slaying, then firing at Reeva Steenkamp as she cowered behind his locked bathroom door with no hope of escape.
"She couldn't go anywhere," Prosecutor Gerrie Nel told a packed courtroom Tuesday. "It must have been horrific."
Weeping uncontrollably, Pistorius listened as his words were read out in court by his lawyer during the opening of a two-day bail hearing, his first public account of the events surrounding the shooting death of Steenkamp, a 29-year-old model and reality TV star who had spoken out against violence against women.
"I fail to understand how I could be charged with murder, let alone premeditated murder, as I had no intention to kill my girlfriend, Reeva Steenkamp," Pistorius said in the sworn affidavit. "I deny the aforesaid allegation in the strongest terms."
It was the first time that the prosecution and Pistorius provided details of their radically divergent accounts of the killing, which has shocked South Africans and fans worldwide, who idolized the 26-year-old track star known as the Blade Runner for overcoming his disability to compete in last summer's London Olympics.
Nel said Pistorius committed premeditated murder when he rose from his bed after a fight with Steenkamp, pulled on his prosthetic legs and walked about 20 feet from his bedroom to the locked toilet door and pumped it with four bullets, three of which hit the model.
That contradicted the runner's statement, read aloud by defence lawyer Barry Roux, who described how the couple spent a quiet night together in the athlete's upscale home in a gated community in the capital of Pretoria, then went to sleep around 10 p.m.
Sometime before dawn, Pistorius said he awoke, and walking only on his stumps, pulled a fan in from an open balcony and closed it. That's when he said he heard a noise and became alarmed because the bathroom window, which had no security bars, was open and workers had left ladders nearby.
"It filled me with horror and fear," Pistorius said in the statement.
"I am acutely aware of violent crime being committed by intruders entering homes," he said. "I have received death threats before. I have also been a victim of violence and of burglaries before. For that reason I kept my firearm, a 9 mm Parabellum, underneath my bed when I went to bed at night."
Too frightened to turn on a light, Pistorius said, he pulled out his pistol and headed for the bathroom, believing Steenkamp was still asleep "in the pitch dark" of the bedroom.
"As I did not have my prosthetic legs on and felt extremely vulnerable, I knew I had to protect Reeva and myself," he said, adding that he shouted to Steenkamp to call the police as he fired at the closed toilet door.
It was then, Pistorius said, that he realized Steenkamp was not in bed.
He said he pulled on his prosthetic legs and tried to kick down the toilet door before finally giving up and bashing it in with a cricket bat. Inside, he said he found Steenkamp, slumped over but still alive. He said he lifted her bloodied body and carried her downstairs to seek medical help.
But it was too late. "She died in my arms," Pistorius said.
"We were deeply in love and I could not be happier," the athlete said. "I know she felt the same way. She had given me a present for Valentine's Day but asked me only to open it the next day."
Pistorius broke down in sobs repeatedly as his account was read, prompting Chief Magistrate Desmond Nair to call a recess at one point.
"Maintain your composure," the magistrate said. "You need to apply your mind here."
"Yes, my lordship," Pistorius replied, his voice quivering.
Nair adjourned the case until Wednesday without ruling on whether Pistorius would be granted bail. However, he said the gravity of the charge — which carries a mandatory life sentence — meant the athlete's lawyers must offer "exceptional" reasons for bail to be granted, making his release unlikely.
Roux, the defence lawyer, said there was no evidence to substantiate a murder charge. "We submit it is not even murder. There is no concession this is a murder," he said.
The prosecutor disagreed.
"It is our respectful argument that 'pre-planning' or premeditation do not require months of planning," Nel said. "If ... I ready myself and walk a distance with the intention to kill someone, it is premeditated."
Hundreds of kilometres from the Magistrate's Court, a memorial service was held for Steenkamp in the south coast city of Port Elizabeth. Six pallbearers carried her coffin, draped with a white cloth and covered in white flowers, into the church for the private service and cremation.
Relatives recalled how the model with a law degree had campaigned against domestic violence and had planned to don black for a "Black Friday" protest in honour of a 17-year-old girl who was recently gang-raped and mutilated.
What "she stood for, and the abuse against women, unfortunately it's gone right around, and I think the Lord knows that statement is more powerful now," said her uncle, Mike Steenkamp.
South Africa has some of the world's worst rates of violence against women and the highest rate in the world of women killed by an intimate partner, according to a study by the Medical Research Council, which said at least three women are killed by a partner every day in the country of 50 million.
Since the shooting, several of Pistorius' sponsors have dropped him. On Tuesday, Clarins Group, which owns Thierry Mugler Perfumes, said it would withdraw all advertising featuring the Olympian. A cologne line with the company, called A(asterisk)Men, bears his image.
Associated Press writer Michelle Faul in Johannesburg and AP photographer Schalk van Zuydam in Port Elizabeth, South Africa, contributed to this report.
Jon Gambrell can be reached at www.twitter.com/jongambrellAP. Gerald Imray can be reached at www.twitter.com/geraldimrayAP.