Oscar Pistorius returns to the dock on Monday after a month of psychiatric tests to determine whether mental illness played any part in his actions on the night he shot dead his girlfriend.

The Paralympian will be back in the high court in Pretoria, the capital of South Africa, after a six-week gap that left one of the most world's most eagerly watched murder trials in limbo.

Pistorius is accused of murdering Reeva Steenkamp, a model and law graduate, at his home on Valentine's Day last year. The 27-year-old denies the charge and insists he opened fire by accident after mistaking her for an intruder.

Pistorius, who has since been staying at his uncle's mansion, was assessed as an outpatient over 30 days at Weskoppies psychiatric hospital in Pretoria.

On Monday the trial judge, Thokozile Masipa, is expected to receive the reports of a panel of one psychologist and three psychiatrists who evaluated whether the athlete was suffering a generalised anxiety disorder that could have impaired his ability to distinguish right from wrong when he shot Steenkamp through a locked toilet door.

One of the psychiatrists, Dr Leon Fine, was hospitalised on Thursday after reportedly suffering a heart attack but this is not expected to delay the resumption of the trial.

Nathi Mncube, a spokesman for the National Prosecuting Authority, told the Saturday Star newspaper: "We are expecting the reports to be handed in on Monday and the case should proceed. How we will proceed will be determined by the judge and by the outcome of the reports. But Pistorius has to be at court."

On 20 May the court ruled that Pistorius's observation would inquire if he was "at the time of the commission of the offence criminally responsible" and if he could appreciate the "wrongfulness of his actions and act according to that appreciation".

The prosecutor Gerrie Nel has alleged that Pistorius killed the 29-year-old model after an argument and is an arrogant gun obsessive who refuses to take responsibility for his actions. But he requested an independent inquiry into his state of mind after a forensic psychiatrist, Dr Merryll Vorster, testified that Pistorius's generalised anxiety disorder, combined with his physical vulnerability – he had both lower legs amputated as a baby – could have affected his actions.

Vorster, a defence witness, told the court: "He certainly was able to appreciate the difference between right and wrong, but it may be that his ability to act in accordance with such appreciation was affected by this generalised anxiety disorder."

Kelly Phelps, a senior lecturer in the public law department at the University of Cape Town, told the Associated Press that if the panel backed Vorster's diagnosis it could add weight to Pistorius's account and compel the judge to consider the question: "Is it more likely that he is telling the truth about what occurred on that night?"

Even if the judge rules that Pistorius is guilty despite any disorder that he is suffering, Phelps added, the diagnosis could be a mitigating factor when he is sentenced.

"That is the area of law that is often referred to as diminished responsibility," she added.

Once Masipa receives the conclusions from the mental health experts, it is thought the defence will call around three more witnesses, prior to closing arguments and Masipa's deliberation on a verdict. If, however, the experts who observed Pistorius are not unanimous in their conclusions, the judge can call them to the stand to clarify their findings.

There are no juries at trials in South Africa, so the fate of the "blade runner" will ultimately be decided by the judge, assisted by two assessors. If found guilty of murder, Pistorius could face life imprisonment. If he is acquitted of that charge, the court will consider an alternative charge of culpable homicide.