The prosecution in the Oscar Pistorius murder trial has formally requested the athlete undergoes further psychiatric evaluation for a "general anxiety disorder". Under cross-examination, defence psychiatrist Dr. Merryl Vorster told the court that Pistorius's anxiety would have given him a heightened fear of crime.

The judge will say how long she needs to consider the prosecution's application, and will adjourn the trial until she makes a decision.

If Pistorius was found to be suffering from a mental illness, he could be held not criminally responsible for his girlfriend Reeva Steenkamp's death and found not guilty by reason of "mental illness or intellectual disability".

It comes after Dr. Vorster told the court Pistorius is a "distrusting and guarded" person who is "hyper-vigilant" about security.

Explaining the nature of generalised anxiety disorder (GAD), Dr. Vorster said "It may impact on your capacity to live a normal lifestyle. By definition generalised anxiety disorder is a psychiatric disorder, so one can say it's a mental illness. But one has to look at the impact of that diagnosis on the individual's capacity to live and socialise".

When questioned by Mr. Nel, the psychiatrist said "He (Pistorius) was still able to function at a high-level and he still did socialise. He had distress because of his anxiety disorder but he was at that stage, still able to continue with his life".

Dr. Vorster also felt he was more concerned about personal safety than other South Africans, by locking himself in his bedroom at night.

But Mr. Nel questioned why the defendant, if he had been anxious about security, had not repaired a broken downstairs window that did not have bars on it.

Dr. Vorster is expected to be one of the last witnesses to be called by Pistorius' defence team.

Pistorius is accused of killing Ms. Steenkamp in a premeditated attack at his home in Pretoria, South Africa, on Valentine's Day last year.

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