ANU student mentally impaired at time of bat attack: psychiatrist

Alex Ophel, 19, told a forensic psychiatrist that he did not think about using a knife in the attack that injured four classmates and his tutor in a statistics tutorial on August 25 last year.

Mr Ophel is on trial in the ACT Supreme Court on five counts of attempted murder.

He has pleaded not guilty by reason of mental impairment.

The court has previously heard Mr Ophel had planned to kill all but one of his classmates with a baseball bat, repeatedly rape one surviving woman, before running through the Australian National University campus while covered in blood.

Mr Ophel's plea means the Supreme Court jury must decide whether the defendant meets the threshold for the defence of mental impairment, which is that he could not reason with a moderate degree of sense and composure about whether the conduct, as perceived by reasonable people, was wrong.

ACT deputy director of public prosecutions Shane Drumgold argues the defendant had shown a high degree of reasoning and control in the way he planned and executed the ambush.

However, defence barrister John Purnell, SC, said Mr Ophel had felt an "alien presence", or "higher being", which had pushed him to carry out the attack.

The court on Thursday heard from forensic psychiatrist, Dr Jeremy O'Dea, who said he believed Mr Ophel could not reason at the required level at the time of the alleged offences, and the defence of not guilty by way of mental was available.

Dr O'Dea said he had diagnosed Mr Ophel as having schizophrenia, with two paraphilic disorders, including psycho sadistic disorder - where he prefers non-consenting sexual activity.

Dr O'Dea said the defendant had likely desensitised himself to violence by watching too much pornography and graphic material on the internet while his sexuality was developing as a teenager.

Dr O'Dea said the disorder could disappear if the level of exposure reduced.

The trial continues.