The prosecutor also claims that general anxiety disorder is tantamount to mental illness. (The psychiatrist disagreed with this and stated Oscar is not mentally ill.) In my view, the prosecutor is trying to buy time to save his losing case. The law (Section 78 of the Criminal Procedures Act) requires both that a mental disorder be present and that the person is incapable of appreciating the wrongfulness of his actions. The judge has taken the matter under advisement, but I suspect she will reject the state's request.
The vulnerability issue goes to the culpable homicide charge. The test is what a reasonable person is Oscar's situation would do under the same circumstances. But is the test the average Joe on the street, or the average double amputee who has experienced a life of vulnerability and has a greater fear of of criminals?
The psychiatrist testified as to Oscar's vulnerability -- why he might believe he was in danger when he was not, and why someone in his situation (a double amputee) might approach and confront, rather than flee from the perceived danger. One reason: On his stumps, he had no ability to flee. The only recourse was to confront.(Given the option of "fight or flight", only the "fight" option was available to him.
The point is that Oscar's reactions to situations would be different than the average Joe on the street because of his disability and generalized anxiety disorder. Dr. Vorster testified, "In my opinion Oscar Pistorius' reaction to the perceived threat should be considered in light of his physical disability and his anxiety disorder."
She also said that Oscar's depressive state didn't begin until after the shooting and that Oscar has repeatedly expressed his feeling of remorse after the shooting. She said his memory is good, and he has no intellectual incapacity. In her opinion, Oscar's reactions in court have been real, not feigned.
Dr. Vorster has a PH.d in forensic psychiatry and has worked at the hospital for the criminally insane. She's a professor. Clearly, she knows the difference between an anxiety disorder and mental illness.
(Sources: live twitter feeds of journalists at the trial.)