The 27-year-old double amputee told his trial in Pretoria he had heard noises from the toilet and thought an intruder was coming out.
“Before I knew it, I had fired four shots at the door,” Oscar Pistorius said.
The trial of the athlete, who could face life imprisonment if convicted of murder, was adjourned until Wednesday after he broke down crying.
The Paralympic athlete denies deliberately shooting Reeva Steenkamp on Valentine’s Day last year.
On his first day on the stand, on Monday, Oscar Pistorius made a tearful apology to Reeva Steenkamp’s family.
The prosecution alleges that Oscar Pistorius killed his girlfriend after an argument with her.
In the early hours of February 14, 2013, Oscar Pistorius 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 Reeva 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 Reeva 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, Oscar 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 athlete broke down, the judge adjourned the trial.
Earlier, Oscar Pistorius described how the couple had spent a quiet evening together on February 13, Reeva Steenkamp doing some yoga as he spoke to his cousin on the phone.
He had then watched TV in bed with his head resting on her stomach and she would occasionally show him photos of cars she was looking at on her phone, he said.
Oscar Pistorius said that they had bought Valentine’s Day gifts for each other. He had bought her a bracelet and they had been due to go the jewellers’ to collect it the next day, he said.
Reeva Steenkamp, a 29-year-old model, reality TV celebrity and law graduate, was hit by at least three bullets while in the toilet cubicle of Oscar Pistorius’s home in Pretoria.
Known as the Blade Runner, Oscar Pistorius holds six Paralympic medals and competed in the 2012 Olympic Games.
There are no juries at trials in South Africa, and his fate will ultimately be decided by the judge, assisted by two assessors.
Even if he is acquitted, South African law stipulates that the court must consider the separate, lesser charge of culpable homicide, or manslaughter.
If convicted on this charge, Oscar Pistorius could face between 6 and 15 years in prison.
Oscar Pistorius also faces charges of illegally firing a gun in public and of illegally possessing ammunition, which he denies.
PEzI2RlsC9I cMMdyuXfFUgImage source: Wikimedia Commons President-elect Donald Trump celebrated his election victory at the Ultimate Fighting…
Millions of voters across the US chose to return Donald Trump to the White House…
Donald Trump declares victory in the US election as he addresses jubilant supporters in Florida.…
Stocks around the world are rising as Donald Trump appears to be on the cusp…
Donald Trump has won Pennsylvania, North Carolina and Georgia and taken a lead over Kamala…
Quincy Jones, the celebrated musician and producer who worked with Michael Jackson, Frank Sinatra, Ray…