Oscar Pistorius has an anxiety disorder and was brought up by a mother who regularly phoned police reporting noises in her home, the athlete's murder trial has heard.

Forensic psychiatrist Dr. Merryl Vorster told the court Pistorius viewed his father as an "irresponsible and mostly absent parent".

His mother was a "very anxious person who abused alcohol intermittently" and slept with a gun under her pillow, she said. Pistorius is accused of killing his girlfriend Reeva Steenkamp in a premeditated attack on Valentine's Day last year.

He denies the charge and claims he shot his partner after mistaking her for an intruder.

Dr. Vorster told the court Pistorius, together with his brother Carl and sister Aimee, were "reared to view the world as threatening".

The athlete was "hyper-vigilant" about security and, while in South Africa, "worried about being followed and the security of his home" she said.

He would sleep with his bedroom door locked and appears to be a "distrusting and guarded person", she added.

She also spoke about Pistorius' "fight or flight response", claiming he is more likely to stand up to threatening situations than to flee, as his capacity to do so is limited by his amputations.

On the 30th day of the trial in Pretoria, Dr. Vorster revealed how, as a child, Pistorius was encouraged to behave as normally as possible, despite having surgery on his legs when he was 11-months-old.

The amputation at such a young age would have been perceived as "traumatic assault", she said, as Pistorius "would not have been able to understand why he was in hospital or why he was having an operation".

The insistence of his parents that he should take part in the activities his friends enjoyed "could have resulted in increased levels of anxiety, as the stress of appearing normal continued" she added.

Dr. Vorster is expected to be one of the last witnesses to be called by Pistorius' defence team at his murder trial in Pretoria, South Africa.

Earlier, prosecutor Gerrie Nel finished his intense questioning of ballistics expert Thomas Wolmarans, who was on the stand for three days.

On Friday, the witness recreated the moment Ms. Steenkamp was shot dead by playing the part of the former model in a courtroom reconstruction.

He entered a mocked-up version of Pistorius' bathroom and mimicked the movements he believes the athlete's partner made when the bullets struck her body on Valentine's Day last year.

Earlier in the day, Judge Masipa and lawyers huddled around the door as a court official used a spray to reveal a laser beam set up by prosecutors to show the trajectory taken by one of the bullets.

The trial continues.