It was a spectacle in the courtroom today as Oscar Pistorius took the stand and for the first time told his version of events from the night he shot and killed his girlfriend. Midway through his... See More
It was a spectacle in the courtroom today as Oscar Pistorius took the stand and for the first time told his version of events from the night he shot and killed his girlfriend. Midway through his testimony, the olympic star broke down. Actually he not only broke down he fell apart completely. Weeping so hard that the judge actually got up and left the room. ABC's Matt Gutman reports now for "Blade runner on trial." Reporter: A gut wrenching moment. You couldn't see Oscar Pistorius testify but you didn't have to. Accused of murder, Pistorius began sobbing as he described for the first time publicly the moment he found his girlfriend, the model, dead in his bathroom by his own hand. I sat there and I cried. And I, I don't know, I don't know how long. Emotional testimony by inconsoleable man. Could it sway the judge, that he mistook the model for an intruder. On Valentine's day he fired four bullets into the bathroom in his Pretoria home, killing her instantly. Abruptly the judge suspending proceedings apparently to give Pistorius the opportunity to compose himself. But his howls intensified. Pistorius would come back into the court but wouldn't say another word. I cannot responsibly ask the court to carry on today. Reporter: Oscar Pistorius walking out of court after crumpling on the witness stand. In court we watched as he started to sob and then wail. The question in the courtroom and around the country were the agonized howls helping or hurting his case. The man known as the blade runner, ascended olympic heights. For the past month. Sitting in the front bench in the packed pra tore yal courtroom. For days on end, testimony about the body or blood spatter that had Pistorius doubled over, wretching and heaving. Often seen wrapping his hand around his head. Plugging his ears with his thumbs. Today it was the blade runner's turn to describe the scene that night. I thought that there was an intruder into my home. The first thing that ran through my mind. I needed to arm myself. I needed to protect reeva and I and get my gun. Reporter: He says he grabbed the gun beneath his bed. It was pitch black. If the curtains are drawn. Reporter: Testifying he didn't see reeva but called out to her. Just as I left my bed. I whispered for reeva to get down. Phone the police. Reporter: He testified he kau out to her three times but was focused on imagined intruders. At that point I was overcome with fear. Started screaming, shouting. For the intruders to got out of my house. Hearing something in the bathroom he said he saddled in from. I conceived somebody coming out of the toilet. Before I knew it I fired four shots at the door. I kept on shouting for reeva to phone the police. Reporter: She would never answer. She knew she was dead before he found her body. I was KREG ocrying out for the lord to help me. Skrechl I screaming. The defense argued that he felt more vulnerable. Then Pistorius' lead attorney stunning the courtroom. Would you take your prosthesis off and stand next to the door. Showing what Pistorius looks like without his prosthetics. How uncomfortable would some one like that feel when they don't have their prosthetics on? I think quite, quite uncomfortable. Reporter: Tonight we exclusively interviewed the man who has been building Pistorius' prosthetics for over 20years. So how mobile would Oscar be on his -- If it is stony ground or anything look that. Sharp objects. He is not going to be mobile. Trevor Brockman helped make Pistorius the fastest man on no legs but his prowess on prosthetics made him feel vulnerable self-conscious without them. All this drama playing out on a 24-hour cable station which hangs on every word from the now disgraced national hero. He has given very little information to bolster his case. He has the a lot of work to do. David o'sullivan is a legal analyst with the pop-up Pistorius news channel. Wailing and anguish will be felt by some as being incredibly painful, and others as an act. Earlier in testimony, the defense had Pistorius read messages be tween him and reeva, revealing intimate details of a passionate three month long relationship. It says, kiss, kiss means a lot. Often loving. Some times mundane. She sent him sexy selfies. He called her my angel. Sometimes she made him sound menacing and angry. I'm scared of you some times and how you snap at me. Pistorius breaking down as he read. I'm the girl who fallen lo in love with you and wanted to till you this weekend. The goal to undercut prosecution assertions she was afraid of him. When he first took the stand he expressed sadness even remorse for what he calls a tragic accident. I can't imagine the pain and the sorrow and the emptiness I have caused you and your family. O'sullivan is convinced emotional testimony is hurting Pistorius. Didn't think he did that well. He need to rein him self in. He will have to do something, pretty severe now to ensure he doesn't keep breaking down. Reporter: After all Pistorius has but one person to convince. The judge. Who must look beyond remorse to determine whether reeva's death was a horrible accident or cold-blooded killing. For "Nightline," I'm Matt Gutman in Pretoria, South Africa.
This transcript has been automatically generated and may not be 100% accurate.