The testimony of pathologist Gert Saayman was interrupted by Pistorius' sobbing and retching, leading to 2 pauses in the court proceedings. The judge halted to enquire if he was doing ok.
The presiding judge imposed a broadcast blackout on Saayman's testimony because of it's graphic nature. The ban included live reporting on Twitter.
Pistorius admits he shot Steenkamp, 29, but says that it was a tragic case of mistaken identity and that he thought she was an intruder who had broken into his home.
In court, Saayman confirmed that Steenkamp died from multiple gunshot wounds, consistent with having been hit in the head, arm and hip by three shots fired through the locked door of a toilet cubicle.
Pistorius appeared deeply physically distressed throughout the testimony, repeatedly making retching sounds and clutching his head in his hands. The track star, 27, appeared at times to try to cover his ears by clasping his hands behind his neck, or he put his fingers in his ears. His brother and sister came to check on him during the brief break in Saayman's testimony.
Saayman is the first expert to testify at the trial, which has so far heard several witnesses who reported hearing a woman screaming before a volley of shots in the early hours of February 14, 2013, at Pistorius' home.
Prof Saayman told the court how Miss Steenkamp was struck four times - on the top right of the head, in the right elbow, in the right hip and also in the webbing of her left hand.
He said any of the three injuries to Steenkamp could have been fatal and all immediately incapacitating. He said it was probably the bullet to the skull that killed her almost immediately. It passed from the top of her head over her right eye to the base of her skull, suggesting that she was not standing when hit, he added.
Saayman said the wounds were consistent with "ranger" bullets, which open up "like the petals of a flower" to cause maximum tissue damage.