As a track athlete, murder-accused Oscar Pistorius is trained to react to sound, his lawyer told the High Court in Pretoria on Friday.
Barry Roux SC, said that having armed himself, Pistorius heard a noise in his toilet and his immediate reaction was to pull the trigger.
Contravention of Firearms Control Act
"He was standing at the door, vulnerable, anxious with his finger on the trigger and when he heard a noise, bang", said Roux, referring to shots Pistorius fired.
Read: All said and done, we still don't know WHY Oscar shot Reeva
Pistorius is charged with murdering his girlfriend Reeva Steenkamp on Valentine's Day last year.
He shot her through the locked door of his toilet at his Pretoria home.
Pistorius has denied guilt, saying he thought she was an intruder about to open the door and attack him. The State contends he shot her during an argument and it was premeditated.
Pistorius is also charged with three contraventions of the Firearms Control Act, one of illegal possession of ammunition and two of discharging a firearm in public. He has pleaded not guilty to these charges.
'Anxious and fearful'
We are not making the submission that the accused did not arm himself," Roux told the court in his closing arguments on Friday.
"He armed himself. He went to the toilet. He foresaw that it might be necessary to fire the shots. He was anxious and fearful," said Roux.
Read: Pistorius has no mental defects
The court simply had to decide whether the action to shoot at the door was simply reflex or whether it was reflex combined with the cognitive.
If the shooting simply happened due to reflex action, then this would prove that Pistorius lacked capacity.
If it was reflex and cognitive combined, then the court should explore what the thought behind the action was, said Roux, adding that the thought in Pistorius's mind that day was that he was in danger.
Submitting his closing arguments on Thursday, prosecutor Gerrie Nel said Pistorius had shot at the door knowing Steenkamp was behind it.
He called Pistorius an appalling witness who had tailored his evidence.
On Friday, Roux said the evidence of ballistic expert Captain Chris Mangena showed Pistorius was not directly in front of the toilet door when he shot at it, but rather at the bathroom door.
"This proves that he was actually scared and not trusting of the person who was in that toilet," said Roux.
He was about two metres away from the door when he fired, fatally wounding Steenkamp.
Referring to the Whatsapp messages between Steenkamp and Pistorius, Roux dismissed Nel's suggestion that the 10 percent "unhappy" messages between the two were the messages that carried the most weight.
Steenkamp had sent a message to Pistorius on January 27, 2013 where she said she was scared of him.
On February 7, 2013, she sent another message explaining that she was unhappy with him.
Roux argued that the subsequent messages were affectionate.
Read: What do Reeva's messages mean?
A security guard who testified in the trial told the court that when he called Pistorius shortly after the shooting at his residence, Pistorius told him that "everything was OK".
Roux defended Pistorius on Friday and said there were reasons for this.
Pistorius could have already received help from one of his neighbours who was a doctor, the paramedics had already been called, and he could not speak to the guard because he was crying.
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