Oscar Pistorius broke down in tears as he described the moment he pulled the trigger and fired four fatal shots at girlfriend Reeva Steenkamp, his murder trial heard.
The athlete told the court he was paralysed with fear thinking an intruder had entered the house before he opened fire through a locked toilet door, killing Ms Steenkamp in the early hours of Valentine's Day last year.
"I wasn't sure where to point the firearm," he said. "My eyes were going between the windows and the toilet. I stood for some time.
"I just stayed where I was and kept on screaming. Then I heard a noise from inside the toilet that I perceived to be somebody coming out of the toilet. Before I knew it, I had fired four shots at the door."
Sobbing uncontrollably and wailing, he described the moment he realised Ms Steenkamp wasn't in bed and smashed down the toilet door to reach her.
By the time Pistorius entered the toilet, Ms Steenkamp "wasn't breathing", Pretoria's High Court heard.
Earlier, the athlete had stripped off his prosthetic legs, struggling to move and maintain balance on his stumps, as he sought to demonstrate his walking ability without them.
Describing the events leading up to Ms Steenkamp's death, Pistorius said he heard a window sliding open in his bathroom in the early hours of 14 February, which he said convinced him an intruder was inside the house and that he needed to arm himself and "protect Reeva".
"That's the moment that everything changed," he said. "I thought that there was a burglar that was gaining entry to my home."
The athlete said the room was completely dark, except for a small LED light, and he was alarmed by the sound of a door slamming shut as he made his way along the passage leading to the bathroom.
"Just before I got to the bathroom, I heard a door slam. It could only have been the toilet door," he said. "It confirmed that there was a person or people inside the bathroom at that time."
He added: "I was overcome by fear. I screamed at the person to get out. I screamed at Reeva. I was constantly aware this person could come at me at any time. I did not have my legs on. Just before I got to the bathroom, I stopped shouting."
Earlier in his evidence, Pistorius explained that he had locked the bedroom door, as he did "every" night, and placed his cricket bat, which he later used to smash down the toilet door, against it. He had taken his prosthetic legs off so they "could air" and placed them close to him.
The athlete told the court Ms Steenkamp cooked him dinner and they ate together at around 7pm. He went to his room just before 8pm and opened the balcony because it was "very humid".
The athlete said he fell asleep between 9pm and 10pm.
Pistorius told the court he woke up in the early hours of 14 February because it was "extremely warm" in the bedroom.
He added: "I noticed that the fans were still running and the door was still open. Reeva was still awake. She rolled over to me and said 'Can't you sleep my baba?'", to which he replied: "No I can't, not tonight".
He grabbed a fan, locked the sliding doors and then drew the curtains.
Pistorius returned to the room and heard the sound of "window sliding open", the court heard.
He interpreted the noise as if someone had climbed inside the house from the bathroom window. Pistorius claims he shot Ms Steenkamp in a case of mistaken identity, thinking she was the intruder.
Earlier in the day, Pistorius described how he was "besotted" with Reeva Steenkamp as he answered questions about the phone messages they had sent each other in the days and weeks prior to her death.
The athlete began by reading a conversation from the mobile messaging service WhatsApp, in which the couple argued over an incident that took place at an engagement party, where he accused her of flirting with other men and demanded they leave early.
In late January, the court was told Ms Steenkamp sent a message saying she felt "picked on" and was "sometimes scared" of him.
Referring to the message, Pistorius said: "My lady we were at an engagement party. It was a bad day in our relationship."
The athlete told the court he saw the model speaking to a man he didn't know and felt "insecure and jealous". Pistorius said he "wasn't kind" to her as he "should have been".
He said the couple had some disagreements but insisted they were in a loving relationship, and often exchanged messages of affection and compliments. He often referred to her as "my angel".
Pistorius told the court he was "besotted" with Ms Steenkamp and suggested he was "more into her" at times, than she was into him. He said the model and law graduate understood his needs as an athlete and was very supportive of him.
For two hours, Pistorius sat on the stand, occasionally holding back tears, reading out page after page of Whatsapp messages shared between the pair, as his defence counsel Barry Roux sought to portray a loving couple in a loving relationship.
He also spoke of the first time he met Ms Steenkamp in November 2012. He denied he had cheated on former girlfriend, Samantha Taylor, when he met Ms Steenkamp, saying the previous relationship had ended. At the start of the trial, the 20-year old student and part-time model claimed Pistorius had cheated on her with Ms Steenkamp.
Soon after, Ms Taylor posted, and then deleted, a tweet saying: "Last lies you get to tell. You better make it worth your while".
Yesterday, an emotional Pistorius began his testimony by apologising to the Steenkamp family.
"I will start my evidence by tendering an apology," he said. "I would like to apologise to Mr and Mrs Steenkamp, her family and friends."
"I can't imagine the pain and the sorrow and the emptiness I have caused you and your family.
"You're the first people I think of when I wake up. You're the first people I pray for. I was trying to protect Reeva. When she went to bed that night, she felt loved."
Pistorius revealed that he has been taking anti-depressants since the accident happened, and other medication to help him sleep at night.
"I'm scared to sleep," he said tearfully. "I have terrible nightmares about what happened that night. I can smell blood. I wake up terrified."
- UK Independent