In a strong rebuke of the argument by Paul Douglas Peters that his August 2011 attack on the 18-year-old was the result of bipolar disorder, drinking and depression, District Court Judge Peter Zahra said it was carried out carefully after significant preparation.

"He went into this place with precision ... with his balaclava on and the device in his backpack," Judge Zahra said, referring to the Pulver family's multimillion-dollar Mosman home.

"Within a couple of minutes the victim, studying for her exams, was made compliant by what she was confronted with. In my mind he planned this and implemented it with precision."

The sentencing judge also disputed the claim that the extortion note placed around Ms Pulver's neck, in which Peters falsely stated that he was a "green beret munitions specialist", was the bizarre ramblings of a sick man.

"I think the intention was to place the victim and possibly others in extreme fear for their lives," he said of the note.

But Peters' barrister, Tim Game, SC, said that psychiatric experts had found that his client was suffering from bipolar disorder and depression, had an obsessive personality, and that these had significantly contributed to his behaviour.

"This was behaviour that was bizarre in the extreme," Mr Game said.

"There were no instructions to pay any particular sum of money to anyone ... it was not rational, logical behaviour.

"It is open to your honour to find, on the balance of probabilities that [Peters'] personality had substantially disintegrated. You're talking about someone who is completely isolated ... has no social contact with their family or friends, and is obsessively writing a novel ... That does go to a substantial reduction in criminal culpability."

In March this year, Peters pleaded guilty to aggravated break and enter and detaining for advantage. According to the police statement of facts tendered in court, Peters told detectives he had been going to the Pulvers' Mosman street for a week before the extortion attempt.

In the mid-afternoon on August 3, Peters walked through the front door of the home wearing a rainbow balaclava and carrying a baseball bat and a backpack.

He confronted Ms Pulver and told her: "I'm not going to hurt you." Peters then removed a black box from the backpack and tied it around his victim's throat, along with a USB stick and a two-page letter.

In the document, Peters claimed he was a "green beret munitions specialist" and that the box contained "powerful new technology plastic explosives".

Police eventually tracked Peters down in a small town in the US state of Kentucky.

The sentencing hearing continues.