PRETORIA, South Africa -- Reeva Steenkamp, the 29-year-old model and girlfriend of South African Olympic athlete Oscar Pistorius, had a sports bag packed with her clothes, ready to leave his house, the night he fatally shot her, prosecutor Gerrie Nel told Pretoria’s high court Monday.

The only items not yet packed were a pair of jeans and a pair of flip-flops. Pistorius, on trial for murder, denied there had been a quarrel and she was about to leave.

Pistorius, who contends he shot at the enclosed toilet in which Steenkamp had locked herself because he believed an intruder was there, told the court he screamed at the imagined stranger to get out of his house.

As he recounted the words, Pistorius broke down, weeping in a high-pitched tone. Nel suggested that Pistorius screamed at Steenkamp to get out of his house, a claim the athlete denied.

Under days of cross-examination, Pistorius has frequently made mistakes, contradicted himself and expressed uncertainty. At times, his memory for detail was razor sharp, but when explaining his decision to fire four shots through the toilet door, killing Steenkamp, Pistorius has been vague, insisting simply that he didn’t have time to think, didn’t intend to kill anybody and that the incident was an “accident.”

But his insistence that he formed no intent to shoot may be digging him into a bigger hole, according to legal experts. They say in doing so, he appears to have abandoned his defense that he shot in self-defense. Instead he seems to be claiming that the action of shooting was involuntary and accidental.

For the self-defense argument to apply under South African law, Pistorius would have intended to shoot the intruder, and his task in court would have been to show his fear for his life was reasonable.

“Is it your defense that you fired at the perceived attacker?” Nel asked and Pistorius said no. He insisted it would have been an accident, even if he had shot an intruder.

“It was all an accident?” Nel asked. “That’s correct,” Pistorius responded.

“Your defense has now changed from putative self-defense to involuntary action,” Nel told him, adding that the athlete could have only one defense, not two.

“I didn’t intend to fire but I fired. I pulled the trigger. My firearm was pointing to where I perceived the danger to be,” Pistorius said. The athlete said it never crossed his mind that shooting into the toilet would kill someone inside. He admitted he fired no warning shots.

Involuntary action is a rare defense, involving action taken unconsciously, for example during a bout of sleepwalking or an epileptic fit. [Updated at 11:35 a.m. PDT on April 14: Pistorius first made reference to the fact he did not intend to shoot anyone in testimony last week.]

“During his testimony, he [Pistorius] seems to be claiming that he fired at the toilet door by accident. This is vastly different –- a claim of 'accident' amounts to a claim of involuntariness,” wrote professor James Grant of Witwatersrand University on a legal website Sunday.

Grant said if Pistorius argued that he mistakenly believed he had a right to shoot to kill, this would be a valid defense, “but in his testimony he seems to be changing his defense. He seems to be claiming that the discharge of his firearm was an accident or at the very least, that his conduct was not under the control of his mind,” Grant said.

He added that the involuntary defense was difficult to pursue “because our courts presume that ordinary conduct is voluntary. If you have done something, you need to lay a basis for a claim to have done so involuntarily,” Grant wrote. He added that on the evidence so far, Pistorius had no basis for such a claim.

[Updated at 11:35 a.m. PDT on April 14: South African attorney Tyrone Maseko tweeted that the new defense is “problematic for his team. U have to admit intentional shooting (at intruder) for putative def.” He added in another tweet: “Putative private defense means u believed (wrongly) u were entitled to shoot.”]

Questioned in court about what he based his defense on, Pistorius grew tearful – one of several occasions during the day.

“I’ve given a reason why I fired," he said. "I thought somebody was coming out to attack me. I fired in the direction I thought the attack was coming from.”

Nel told him he fired at Steenkamp as she stood in the toilet, facing the door and talking to him.

“I did not fire at Reeva,” he said, weeping.