Oscar Pistorius has said, had his girlfriend Reeva Steenkamp spoken, he would not have pulled the trigger.
The Paralympian told the court in Pretoria that he fired his gun "by accident" fearing he was about to be attacked by an intruder.
On the night of February 13, 2013, Pistorius fired four shots at the bathroom door of his flat, after hearing a disturbance from inside.
Fighting back tears, the 27-year-old said: "When I heard a noise, I didn't have time to think and I fired my weapon. It was an accident. If Reeva had come out or she had spoken to me I wouldn't have fired. The noise coming from the bathroom made me pull the trigger."
The world famous athlete has denied charges of murder, claiming that he did not know Steenkamp had got of bed and gone to the bathroom.
During the second day of cross-examination by the prosecution, the double amputee recounted in detail the events of that night. He explained he woke up during the night and got out of bed to close the doors to a balcony, shut the curtains and moved the fans into the room.
The athlete said he was unable to see Steenkamp get out of bed and leave the room because he had his back turned and the room was dark.
Pistorius further claims that the duvet and fan in images shown to the court had been moved by police officers after the incident.
However, prosecutor Gerrie Nel claimed Pistorius' version of events "is a lie" and accused him of "adapting" events to suit his account.
Nel further questioned why Pistorius had waited for the public arena of a court room to apologise to Reeva's family.
He told the court: "I am terribly sorry that I took the life of their daughter. I didn't think they would want to see me."
The sports star admitted to having an interest in guns and said that due to the high crime rate in South Africa, he always had a handgun in his possession for his own security and usually had a bullet in the chamber.
The court heard Pistorius had ammunition belonging to his father in the safe at his home, for which he did not have a licence. He also had an extra magazine in his bedside drawer, which was found when he was arrested.
The prosecution have portrayed the athlete as selfish and prone to tantrums, citing text messages in which Steenkamp suggested she was "scared" of his reactions.
He read from one message in which Steenkamp said: "I've been upset with you for two days now... I'm scared of you sometimes'. Why would she be scared of you?"
Pistorius replied: "I think she's scared of the feelings that she had for me, she says 'I'm scared of you sometimes and how you snap at me and how you will react to me'. I never shouted or screamed at her. It hurt her feelings about the way I would react."
Dismantling Pistorious's version of events Nel said his account was "so improbable that nobody would ever think it was possible."
The sportsman was in a relationship with Steenkamp for four months.
Pistorius denies premeditated murder and illegally possessing ammunition and two further counts related to shooting a gun in public in separate incidents prior to the killing.