Oscar Pistorius is depressed, suffering from post-traumatic stress disorder, and is a suicide risk, the doctors who spent a month evaluating his mental health concluded.
But he does not appear to have a history of abnormal aggression or psychopathic tendencies linked to "rage-type murders in intimate relations," they found.
The conclusions, read at the athlete's murder trial on Wednesday, are a "slam-dunk for the defense," CNN legal expert Kelly Phelps said.
The double amputee sprinter is on trial for killing his girlfriend Reeva Steenkamp in his home last year.
He admits killing her but says he mistook her for a burglar and thought he was defending himself.
The prosecution says the two had an argument and he killed her intentionally.
The psychiatric report seemed to suggest that Pistorius's version of events was plausible.
"When Mr. Pistorius's appraisal of the situation is that he might be physically threatened, a fear response follows that might seem extraordinary when viewed from the perspective of a normal bodied person, but normal in the context of a disabled person with his history," the doctors found.
One of the questions Judge Thokozile Masipa must consider in determining her verdict is whether Pistorius behaved reasonably in the circumstances.
Several witnesses have testified that Pistorius tends to arm himself and go towards danger, rather than away from it, when he thinks he is under threat.
The track star's specialist sports doctor testified Wednesday after defense lawyer Barry Roux read the mental health report.
Wayne Derman said that Pistorius was "hypervigilant."
The trial restarted Monday after a monthlong break when Pistorius was evaluated by mental health experts at the prosecution's request.
They found he was not mentally incapacitated when he shot and killed Steenkamp.
An independent panel of doctors said that Pistorius was, at the time he shot Steenkamp, not mentally ill or incapacitated in any way that would make him "criminally not responsible of the offenses charged."
The report added that "Mr. Pistorius was capable of appreciating the wrongfulness of his act."
Had the doctors deemed Pistorius mentally incapacitated during the shooting, the trial would have immediately ended in a verdict of not guilty by reason of mental illness.
At the trial's conclusion, Judge Masipa will have to decide whether Pistorius genuinely made a mistake or killed Steenkamp intentionally.
If she does not believe the athlete thought there was an intruder, she will find him guilty of murder and sentence him to a prison term ranging from 15 years to life. South Africa does not have the death penalty.
If Masipa accepts that Pistorius did not know Steenkamp was the person he was shooting at, she could find him guilty of culpable homicide, a lesser charge than murder, or acquit him, according to CNN legal analyst Kelly Phelps.
A verdict of culpable homicide would leave the sentence at Masipa's discretion.