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.
According to the findings by an independent panel of doctors, Pistorius did not suffer from a mental defect or mental illness at the "time of the commission of the offense that would have rendered 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 Thokozile 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 at least 15 years in prison and possibly 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.