Pretoria, South Africa (CNN) -- Track star Oscar Pistorius broke down in court Thursday, the fourth day of his murder trial, as a neighbor described the grisly scenes when he tried to save the athlete's girlfriend after a fatal shooting on Valentine's Day 2013. The amputee sprinter, 27, nicknamed "Blade Runner," has pleaded not guilty to all four counts against him, saying the killing of model Reeva Steenkamp, 29, was a tragic error and he mistook her for an intruder. In graphic testimony, witness Johan Stipp, a doctor who lived close by, said he went to Pistorius' residence after hearing shots fired. He said he saw Steenkamp mortally wounded, her brain tissue mixed with blood and Pistorius praying for her to live.
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NEW: "He definitely wanted her to live, " witness says about Oscar Pistorius
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Witness says he saw Reeva Steenkamp had been mortally wounded
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"I thought she was a burglar and I shot her," witness quotes Pistorius as saying
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Defense attorney grills another witness on notes taken of fatal shooting
The prosecution has put up several witnesses who live near @placeholder and say they heard shouting before the four gunshots that night, while his defense attorney has grilled them relentlessly to raise doubts about their version of events.