Rocking back and forth in the dock, Pistorius put his hands over his ears as neighbour and radiologist Johan Stipp recounted how he entered his house to find the distraught Paralympian bent over, attempting to resuscitate his girlfriend.
Stipp noticed a wound on Steenkamp's right thigh, right upper arm, and "blood and hair and what looked like brain tissue intermingled with that" on top of the skull.
Amid the scene of horror, Stipp said he quickly realised the 29-year-old model would not survive the injuries.
"I opened her right eyelid, the pupil was fixed, dilated and the cornea was milky, in other words it was already drying out, so to me it was obvious that she was mortally wounded."
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During the testimony, sobbing could be heard around the courtroom as Steenkamp's family and friends sat disconsolately arm-in-arm.
Stipp continued: "While I was trying to ascertain if she's revivable, Oscar was crying all the time, he prayed to God to please let her live, she must not die."
"I couldn't do anything for her, she was way too seriously injured for that."
At one stage, seeing Pistorius leave Steenkamp's body to go upstairs, Stipp also said he wanted to locate the weapon, fearing the sprinter may have been a danger to himself.
"Oscar was emotionally very, very upset and I didn't know the situation in the house so I thought maybe he was going to hurt himself."
When court adjourned, the athlete looked visibly shaken. As his lawyers packed up their bags, his sister Aimee, wearing an outfit of all black, went to sit with him in the dock, her arm around his shoulders.