The murder trial of Oscar Pistorius has been adjourned on the second day of his giving evidence, after the South African athlete started sobbing while describing what happened on the night he shot his girlfriend.
Pistorius said he had picked up his gun because he thought there was an intruder in the house.
"Before I knew it, I had fired four shots at the door," he said.
The BBC reports the trial was adjourned until Wednesday after he broke down crying.
The accused, 27, a double amputee, denies deliberately shooting Ms Steenkamp on Valentine's Day last year.
The prosecution alleges that Mr Pistorius killed his girlfriend after an argument with her.
In the early hours of 14 February 2013, he said he had got up from bed to bring in some fans he had left outside, in order to cool his bedroom.
When he heard a window opening in the bathroom, he said, he thought there was a burglar trying to get in.
Wanting to protect Ms Steenkamp, who was not sleeping, he had gone to get his gun in the dark.
"I whispered to Reeva to get down and phone the police," he said.
He said he then went into the passage without his prosthetic legs and, overcome with fear, started screaming, and shouted for Ms Steenkamp to get to the floor.
The toilet door slammed, reconfirming his belief there was a person or people in the bathroom, the athlete said.
"I heard a noise from inside the toilet, what I perceived to be someone coming out of the toilet," he said tearfully. At that point, he shot at the door.
After the shooting, Pistorius said he had smashed in a door panel to get into the toilet, where he discovered what he had done.
"Whilst I leant over the partition to get in, I saw the key, so I took it and I unlocked the door, and I flung the door open, and I threw it open," he said, sobbing.
"And I sat over Reeva and I cried... and um, I don't know how long... I don't know how long I was there for... She wasn't breathing."
As the accused broke down, the judge adjourned the trial.