The jury deliberating on the case of Australian National University baseball bat attacker Alex Ophel has been discharged, after 21 hours of discussion left them unable to reach a verdict.

Key points: ANU student Alex Ophel faced five counts of attempted murder after attacking classmates with a baseball bat

ANU student Alex Ophel faced five counts of attempted murder after attacking classmates with a baseball bat The jury could not decide whether Mr Ophel was guilty and so were discharged.

The jury could not decide whether Mr Ophel was guilty and so were discharged. Mr Ophel did not dispute the attack happened, but his lawyers argued he was mentally impaired.

Mr Ophel faced five counts of attempted murder after walking into his statistics class at the ANU in August last year, swinging at his tutor and classmates.

The 19-year-old never denied committing the act.

In an interview he claimed the plan was to kill everyone at his statistics class at the Australian National University except for one woman, who he planned to rape.

His tutor was hit in the head, one woman suffered two broken arms and others were also injured before he was restrained.

In the lead-up to the attack he had left a video on his YouTube channel under the name Thane Jekyll, with a cryptic suggestion about disappearing.

He had also left a message on the internet site 4 Chan, saying: "If I were you, I'd keep an eye out down under. It's going a bit batty at this time of the year".

In the hours leading up to the ANU incident, he searched the internet for things like: "How easy is it to kill someone with a baseball bat?", "ACT murder laws" and "ACT life sentences".

Alex Ophel posted a video on his YouTube channel with a cryptic message about disappearing. ( News Video )

Mr Ophel's lawyers said it was a case of "mental illness simpliciter".

A succession of psychiatrists who gave evidence in the trial painted a picture of a disturbed young man who thought he was controlled by higher beings, which controlled his will.

His lawyer John Purnell told the jury his plan was clearly crazy.

"If higher beings played a role in his life would he have done that act?" Mr Purnell asked.

"It is patently clear Alex was mentally ill and mentally impaired."

Dispute over whether Mr Ophel was 'deluded'

The court heard from several psychiatrists, with evidence that Mr Ophel had either been suffering schizophrenia or and early stage of it at the time.

Mr Purnell told the jury he clearly met the test of mental impairment because he didn't know what he was doing was wrong, and couldn't control the actions.

But prosecutor Shane Drumgold painted a darker picture — of a young man under pressure to perform at university who decided to act on a fantasy he'd entertained for several years.

He pointed to comments to friends including one remark that if he didn't get a girlfriend soon he'd have to rape someone.

Mr Drumgold said Mr Ophel did not meet the test for mental impairment, pointing to the internet searches and video in the preparation for the attack.

He told the court Mr Ophel knew the consequences and knew his rights when arrested.

Mr Drumgold also said there was no evidence of delusions before the attack.

Mr Ophel's parents both gave evidence in the trial of a clever younger student, whose marks had waned once he arrived at university.

If there is a new trial, it is unlikely to begin before February next year.