PRETORIA, South Africa — As the girlfriend he shot lay dead or dying in his home, a weeping, praying Oscar Pistorius knelt at her side and struggled in vain to help her breathe by holding two fingers in her clenched mouth, a witness testified Thursday at the double-amputee runner’s murder trial.

Radiologist Johan Stipp recalled Pistorius saying, ‘‘I shot her. I thought she was a burglar. I shot her.”

Continue reading below

The testimony was the first detailed public description of the immediate aftermath of the shooting of Steenkamp, a 29-year-old model, by the Paralympic champion in the pre-dawn hours of Feb. 14 — Valentine’s Day — last year.

As a radiologist, Stipp said he used his expertise to try to save the woman.

‘‘I tried to open an airway,’’ he said.

Sitting on a courtroom bench, Pistorius bent forward and put his hand over his face, then moved them to cover both ears, as Stipp spoke. He stayed that way for a while.

Pistorius is charged with shooting Steenkamp three times through a toilet door in his home. Prosecutors said the athlete intentionally killed Steenkamp after an argument, but Pistorius says it was a mistake and he thought she was an intruder.

‘‘Oscar was crying all the time,” said Stipp. “He was praying to God, ‘Please let her live.’ ”

Pistorius’s lead defense lawyer started the fourth day of the trial by cross-examining another neighbor and questioning whether the man heard a woman screaming and then gunshots.

‘‘‘I’m convinced that I heard a lady’s voice,’’ said the neighbor, Charl Johnson.

A defense lawyer said the sounds were actually Pistorius hitting the toilet door with a cricket bat and the screaming was the distressed athlete calling for help — and there were no sounds from Steenkamp, who had been shot in the head.

The sequence of events is critical. Prosecutors say there was a loud argument before the shooting. Pistorius says there was no argument.