Mr Ophel's defence team made a number of admissions about the attack on day two of his ACT Supreme Court trial on Tuesday.

Mr Ophel, 19, has pleaded not guilty by way of mental impairment to the attempted to murder of five people in his Australian National University statistics class on August 25 last year.

The victims suffered fractured skulls and broken arms in the attack, which only stopped after students managed to restrain Mr Ophel until security and police arrived.

Barrister, John Purnell, SC, said the only issue in contest during the trial would be whether Mr Ophel had been mentally impaired at the time of the incident.

Mr Purnell told jurors that if the answer to that question had been yes, they could return a special verdict of not guilty by way of mental impairment.

In his opening submissions, Mr Purnell warned jurors the evidence in the trial would be shocking and disturbing.

He said his client had felt an "alien presence", or "higher being", which had pushed him to carry out the attack.

Mr Purnell said the defendant believed a presence had been coming that would destroy the world, which only people like him could stop.

The silk said jurors, during the trial, would hear from a number of experts who had diagnosed Mr Ophel with psychiatric disorders, including schizophrenia, and had been psychotic at the time of the attack.

Mr Purnell said the expert evidence would show the defendant could not reason the conduct had been wrong at the time and believed his actions had been morally justified.

The defence barrister urged jurors to look at the evidence fairly, assess it objectively, and make a decision on guilt based on what was before them.

The Crown, however, alleges Mr Ophel had not been mentally impaired, arguing he had shown a high degree of reasoning and control in the way he planned and executed the attack.

In the prosecution openings, jurors heard Mr Ophel had violent sexual fantasies and an obsessions with US school shootings.

ACT deputy director of public prosecutions Shane Drumgold said the defendant had intended to kill his classmates and tutor before raping one surviving woman, preparing for the strike for about one month.

The court heard the defendant, the day before the incident, had searched the internet with terms such as "How easy is it to kill someone with a baseball bat", "ACT murder laws", and "ISIS beheadings".

He also posted a warning on a 4chan forum, which said: "If I were you I'd keep an eye out downunder. It's getting a bit batty this time of years".

Before the attack, he sent friends farewell messages before drinking a cocktail of coffee and port to disinhibit himself, the court heard.

The trial before Chief Justice Helen Murrell continues.