PRETORIA, South Africa – It was the kind of flourish more often seen in courtroom dramas than in real-life murder trials. In the middle of his emotional and harrowing testimony Tuesday, Paralympic sprinter Oscar Pistorius stood up in full view of the packed courtroom, removed his prosthetic legs and demonstrated how very vulnerable and exposed he can be.

The moment came on a grueling day in which a shaky, tearful Pistorius for the first time gave a full account of what he says happened the night that he shot and killed his girlfriend, Reeva Steenkamp. And it went toward bolstering the case the defense is trying to make: that Pistorius, the world’s most celebrated disabled athlete, is at the same time an anxious and physically fragile man who sprayed bullets through the door of his bathroom because he believed someone had broken into his house.

“I was overcome with fear,” he said, speaking of the moment he says he heard noises coming from outside his bedroom in the early hours of Feb. 14, 2013.

It was a hot and muggy night, Pistorius testified, and his air conditioning was not working. He woke up in the middle of the night, spoke to Steenkamp and then – without turning on the lights or putting on his prosthetic legs – went to the balcony next to his bedroom, he said.

Then, he says, he heard a noise.

“My lady, that’s the moment that everything changed,” he told the judge, Thokozile Masipa. “I thought that a burglar had entered my home. Initially I froze. I didn’t know what to do. The first thing that ran through my mind is that I needed to protect myself,” he said, “that I needed to protect Reeva and I.”

Pistorius is accused of murdering Steenkamp by shooting her four times in a fit of violent rage. If convicted of the most serious of the charges, he faces a minimum of 25 years in prison.

He contends that it was a tragic mistake, that he grabbed his gun from under the bed and went in search of intruders.

Even under mild questioning by his own defense lawyer, Barry Roux, Pistorius stuttered, paused, cried and lowered his voice to a whisper. And when he got to the crucial part of his story – the part where he fired through the bathroom door – he began weeping in earnest.

By his account, he believed that Steenkamp had remained in bed, in their dark bedroom, because he had spoken to her before getting up. Apparently, too, he believed she failed to respond to his screams because, hearing him shout that intruders were in the house, she feared for her own safety.

“I was just panicked at this point,” he said, describing how he took the cricket bat he kept in his bedroom and used it to batter down the locked door. “I don’t think I’ve ever cried like that or screamed like that. I was crying out for the Lord to help me. I was crying out for Reeva.”

He bashed the door open, he said, and sat over Steenkamp’s lifeless body. “I sat over Reeva and I cried,” he said – for how long, he cannot remember. “She wasn’t breathing.”

It was then that he broke down completely, convulsing and heaving in sobs, and could not go on.

Pistorius’ lack of composure Tuesday does not augur well for how he will stand up under cross-examination by the prosecutor, Gerry Nel, who is known for his aggressive, unforgiving questioning.