Judge Thokozile Masipa has not yet ruled on the request. Prosecutor Gerrie Nel said he had no other option but to ask for a study of Pistorius' mental health following testimony by a psychiatrist, who said the Olympic runner's anxiety could have shaped the way he responded to perceived threats.
Pistorius has said he killed girlfriend Reeva Steenkamp by mistake last year, fearing that there was an intruder in his home when he fired through a closed toilet door in the early hours of Feb. 14, 2013. The prosecution says he killed her intentionally after an argument.
Psychiatrist Dr. Merryll Vorster said events during Pistorius' life, including the amputation of his lower legs as a baby and his late mother's habit of sleeping with a gun under her pillow, contributed to his "increasing stress."
"Overall, Mr. Pistorius appears to be a mistrustful and guarded person," Vorster testified.
She said the Olympic athlete displayed "escalating levels of anxiety" through his life when she interviewed him this month. Vorster said she also spoke to members of Pistorius' family, some of his friends and his agent.
Pistorius' defense said at the outset of its case that it would show his feelings of "vulnerability" and his disability contributed to him shooting Steenkamp. Pistorius is charged with premeditated murder and faces 25 years to life in prison if convicted.
Vorster's testimony also dealt with what she said was Pistorius' fear of crime and how, because he was a double amputee, he reacted to perceived threats in a different way to other people. She noted Pistorius' mother, who died when he was a teenager, slept with a gun in her bed and also had a fear of being attacked in her home.
Cross-examining Vorster at the start of the eighth week of the trial, prosecutor Nel asked if she was saying Pistorius had a mental illness and should undergo a 30-day period of observation, and if he was changing his defense to one of "diminished responsibility."
Nel also asked the psychiatrist if someone who was suffering from an anxiety order of the kind that she had diagnosed in Pistorius, and also had access to guns, would be a danger to society. Vorster said the person would, indeed, be a danger.
Talking specifically about the shooting of Steenkamp, Vorster said Pistorius was more likely to try and "fight" what he thought was an intruder than run away, because his disability meant it was harder for him to flee. Pistorius was on his stumps when he fired four times through the toilet stall door with his licensed 9 mm pistol, killing Steenkamp.
Imray reported from Stellenbosch, South Africa.