Today was the first time Oscar had to recount the events that led to the death of his girlfriend to the court, something which he did through sobs.
Mr Pistorius described how, in the early hours of the morning, he head a window sliding open in his bathroom.
Explaining that after years of living in South Africa - a country plagued by crime and break-ins - the sport star was frightened and at that moment 'everything changed.'
Grabbing his gun from under his bed, Pistorius said he then told Reeva to take cover as he went to investigate the noise.
'I got to the entrance of the bathroom at the end of the passage where I stopped screaming,' said the athlete.
Oscar Pistorius: 'I will carry it with me for the rest of my life.'
He said that at this point, after calling out for whoever was there to get out of the house, he tried to edge round towards the bathroom.
'Then I heard a noise from inside the toilet that I perceived to be someone coming out of the toilet.'
'Before I knew it I had fired four shots at the door.'
The Paralamypian, who won gold in London 2012, just six months before the tragic incident, said that the noise was so great he carried on shouting for Reeva to get the police.
But after retreating to the bedroom and realising that Reeva was not there, Pistorius says he came to the conclusion that it could be his girlfriend in the bathroom.
Hitting down the door, he found Reeva fatally injured on the floor.