A PANEL of mental health experts has concluded Oscar Pistorius was not suffering from a mental illness when he killed girlfriend Reeva Steenkamp, the athlete's murder trial has heard.

Pistorius' trial resumed after a break of one month during which a psychologist and three psychiatrists also assessed whether the double-amputee runner was capable of understanding the wrongfulness of his act when he shot Ms Steenkamp through a closed toilet door.

The panel's reports were submitted to Judge Thokozile Masipa, and prosecutor Gerrie Nel referred to key parts of the conclusions, noting experts believed Pistorius was "capable of appreciating the wrongfulness of his act" when he killed Ms Steenkamp, a 29-year-old model.

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The evaluation came after a psychiatrist, Dr Merryll Vorster, testified for the defence that Pistorius, who has said he feels vulnerable because of his disability and a long-held worry about crime, had an anxiety disorder that could have contributed to the killing in the early hours of February 14, 2013.

Pistorius testified he opened fire after mistakenly thinking there was a dangerous intruder in the toilet.

Prosecutor Mr Nel has alleged Pistorius, 27, killed Ms Steenkamp after a Valentine's Day argument and has portrayed the South African Olympic athlete as a hothead with a love of guns and an inflated sense of entitlement. But he requested an independent inquiry into Pistorius' state of mind, based on concern the defence would argue Pistorius was not guilty because of mental illness.

Pistorius faces 25 years to life in prison if found guilty of premeditated murder.