Oscar Pistorius' Defense Nears the End of Its Case

A look at what's next in the trial of the Olympic athlete known as "Blade Runner."
2:43 | 05/12/14

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Transcript for Oscar Pistorius' Defense Nears the End of Its Case
And now to Oscar Pistorius, the defense wrapping up its case in his trial for the murder of his girlfriend. The defense and prosecution trying to get inside the mind of Pistorius this morning. ABC's Matt Gutman is right there at the courthouse covering it all for us. Good morning, Matt. Reporter: Good morning, robin. Pistorius' defense going for broke this morning trying to prove his vulnerability by portraying him as someone not only physically but psychologically disabled, as well. Someone with an anxiety disorder. A lone wolf afraid of the world around him and primed to pull the trigger. Oscar Pistorius was a walking powder keg. When exposed to a threat, Mr. Pistorius is more likely to respond with a fight response rather than a flight response. Reporter: For the first time psychiatrists detailed a portrait of a tortured Oscar Pistorius beginning with the amputation of his legs when he was just 11 months old. This type of procedure at this age is perceived by infants as traumatic assault. Reporter: Dr. Meryl vorster testifying off camera trying to explain his itchy trigger finger the night he shot his girlfriend reeva steenkamp saying he had om from a broken home. It appears that his mother was a very anxious person and abused alcohol intermittently. She slept with a firearm under her pillow and there were frequent episodes when the police were called in to investigate noises she had heard. Reporter: He sought to protect himself. He bought a firearm for his own protection. At some stage he had a target at his house and this resulted in him adding extensive security measures at his house. Mr. Pistorius has an anxiety disorder. Individuals with an anxiety disorder work hard to control their environment and be very prepared in order to alleviate their levels of anxiety. Reporter: The more famous he got, said vorster, the harder he worked to control his environment. As he became more and more exposed to being famous and having media attention, he would have had to prepare more and more to not embarrass himself in any way. Reporter: The prosecutor pouncing wondering if Pistorius knew right from wrong. A generalized anxiety disorder is a psychiatric diagnosis. I would not consider it to be a mental illness. In my opinion it would not be something that could be taken into account in terms of looking at his responsibility. Reporter: Now, that psychiatrist making a fine point saying Oscar Pistorius did not right from wrong and was responsible that night but in a way different from a, quote, Normal person. Now, it's up to the judge to decide whether that's enough to make this a mitigating factor in this murder trial. Rob and George. And we will wait and see what happens.

This transcript has been automatically generated and may not be 100% accurate.

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