Prosecutor Gerrie Nel confronted the first defence witness testifying at Oscar Pistorius's murder trial in the High Court in Pretoria on Monday.

Retired pathologist Jan Botha had testified that he believed Pistorius shot his girlfriend Reeva Steenkamp first in the hip, then the arm, then the head in about four seconds, and then she died probably without being able to call out.

Botha, who has two fellowships in anatomical pathology under his belt, presented this evidence to Pistorius's lawyer Barry Roux SC, who has gained a reputation for exhausting every avenue in pursuit of an acquittal for his client.

At the first opportunity, Nel grilled Botha on his theory of the sequence of wounds, occasionally bringing the grey-haired professor to the point of irritation as he said: "I am not a ballistician".

Nel said: "You stood there, you gave evidence, you told the court, you said 'I know what the sequence is'."

"I said 'I believe', I didn't say 'I know', I'm not that presumptuous Mr Nel," Botha reacted.

Nel took Botha through the shot-by-shot sequence of Steenkamp's last moments in the early hours of Valentine's Day last year when Pistorius shot her as she was in the toilet cubicle of his Pretoria home.

Pistorius held his hands over his head when Botha described any anatomical details, but made a quick recovery to watch the adversarial exchanges between the two.

The court adjourned for tea.