Transcript for Oscar Pistorius Murder Trial: Blade Runner Takes the Stand
Great pictures. We'll see more on those. More on the emotional and dramatic testimony from Oscar Pistorius on the stand in his own defense this morning. ABC's Matt Gutman has all the details. I wake up every morning and you're the first people I think of, the first people I pray for. I can't mention the pain and the sorry I caused you and your family and I was simply trying to protect reeva. I can promise you when she went to bed that night she felt loved. Reporter: A broken man, his first whimpered words an apology to reereeva's family. Watching from the bench steenkamp's mother stone-faced. His face quivering and so low the judge asked him to speak up. I don't like doing this to you but I can hardly hear you. I beg your pardon, my lady. I'll speak up. Reporter: It described his fragile mental state. I'm scared to sleep. Reporter: Saying he wakes up every night in a panic. I can smell blood and wake up to being terrified and in a complete state of terror to the point they'd's rather not sleep. Reporter: The man who had purchased a small arsenal of guns before the shooting now terrified of them. I never want to handle a firearm again or so -- I've got a security guard that is outside my front door at night. Reporter: Playing out its case. The marking, disability, evidence relevant to vulnerability. Reporter: Suggesting it will rely heavily on the double amputee's disability and his sense of vulnerability that night. And Pistorius describing his birth defect. I was born with a missing fibula which is one of the two bones between the knee and the knee and the ankle. Reporter: And a mother who always made him feel like he was no different than anyone else. She treated me exactly the same as my brother and my sister. Reporter: Until this, it will last for days. Earlier we saw the lead prosecutor absolutely grill the defense's pathologist, actually belittling him on the stand and told he is going to be absolutely ferocious when he cross-examines Pistorius. Now, the big question is, can Pistorius' story and nerves hold up? Lara. That is the big question. We want to get to our chief legal affairs anchor Dan Abrams for more on this. It's a huge day, so emotional. What do you think of his decision, Pistorius', to start off by apologizing to the steenkamp family. If the judge is going to let him do it, why not. Emotional, powerful. Whether this was murder or an accident he's sorry, you can make an argue. I'd like to believe he felt like he needed to do that. But the key to his testimony will be whether he can survive cross-examination and potential inconsistencies about what time did they go to bed and where was the gun and was there screaming? Those are going to be the key questions he has to address. One thing to do it with your defense team and quite another -- ? Exactly, exactly. What do you make of all the talk about his disability. That's part of the defense. The defense wants to argue that a reasonable person in his position with his disabilities would have more fear than an ordinary personal and so they're saying that has to come into account in the legal standard, as well. So not only is it emotional testimony, powerful testimony how he overcame it and still has issues but related to the legal issues in the case. It was really emotional. It sound like he could barely get through it. He's the one who asked not to be on camera. We see audio only. Interesting Pistorius made the decision and his team to say we don't want him on camera. We want audio only. That is. I want to talk about the first witness. Traditionally it should have been the defendant but instead it was a pathologist. I think it was a scheduling issue, but the pathologist is important in trying to discount a lot of testimony we've heard so far from the prosecution's team and in essence what this pathologist is trying to demonstrate is, don't believe all of what you heard from the prosecution's witnesses suggesting that Pistorius' account doesn't make sense. Dan Abrams, thank you so much. More to come as we know.
This transcript has been automatically generated and may not be 100% accurate.