Paralympian Oscar Pistorius's defence team has sought to show the double-amputee sprinter feels highly vulnerable and acted out of fear, not anger, when he shot dead his girlfriend.
Pistorius has a "split personality", defence lawyer Kenny Oldwadge told the court.
There are "two Oscars", he said -- a world-class athlete and a highly vulnerable individual with a serious disability.
Oldwadge was reading from a psychological report on Pistorius, who underwent 30 days of psychiatric examination before his trial resumed on Monday.
Lawyers defending the 27-year-old, on charges that he deliberately shot and killed model Reeva Steenkamp on Valentine's Day last year, are calling their final witnesses.
Medical expert Wayne Derman testified that Pistorius, known as the Blade Runner for his j-shaped prosthetic limbs, was not always the fearless superhero depicted in sports advertisements.
"Although he loathes to be pitied in any way, the hard truth is that he does not have lower legs," said Derman, chief medical officer of the South African Paralympic Team at the London Olympic Games in 2012.
"You've got a paradox," he said, "of an individual who is supremely able and an individual who is significantly disabled."
During five months of the stop-start trial, Pistorius's lawyers have sought to portray him as manically obsessed with safety, after a difficult childhood with a mother who intermittently abused alcohol, and in the face of high crime levels in South Africa.
Those factors, they argue, help explain his reaction when he shot dead the 29-year-old model and law graduate through a locked toilet door, allegedly convinced she was an intruder.
Derman, who has known Pistorius for six years, said he had an exaggerated reaction to sound because of his training as a professional athlete, where a gun is fired to start a race.
"The athlete is taught not to anticipate, but to react," said Derman.
The expert witness, expected to be the last before the defence concludes its case, said it was Pistorius's unusual "startle magnitude" that "culminated in this horrific tragedy".
The witness, who prosecutor Gerrie Nel accused of bias in favour of Pistorius, was argumentative and indignant on the stand, at times refusing to answer questions.
The trial was adjourned until Monday.
Pistorius faces up to 25 years in South Africa's brutal jails if convicted.