A psychiatrist who assessed the man who attached a fake collar bomb to a Sydney teenager has told a Sydney court it was one of the most difficult cases he has ever encountered.
Clinical psychiatrist Jonathan Phillips told the District Court in Sydney on Wednesday that he believed Paul Douglas Peters was in a psychotic state when he entered the Pulver family home in Mosman in August 2011.
"This is one of the most difficult assessments I have ever had to carry out," Dr Phillips told the court.
"It's unusual for a person with a long and seemingly untroubled life and record to then commit an extremely callous and dangerous act."
Peters, 52, has pleaded guilty to breaking into the home and attaching a fake collar bomb to 18-year-old Madeleine Pulver's neck after cornering her in her bedroom.
An attached document demanded an unspecified sum of money and said the device would explode if tampered with.
The incident sparked a 10-hour police operation before the device was confirmed to be fake.
Peters was arrested in the Kentucky home he had shared with his ex-wife, Debra Peters, in the US a couple of weeks later on August 15.
Dr Phillips, who interviewed Peters, said it was hard to understand how he appeared to act "relatively normally in a number of areas of his life" but then could become "very distorted in his thoughts".
He said he believed Peters suffered from a bipolar disorder and was coming in and out of a psychotic state in the weeks or months prior to the incident.
Peters has told psychiatrists his last memory of the collar bomb event was walking up the steps of the Pulver home.
The court has also heard Peters had taken on the role of a character in a book he was writing, which he was "obsessed" with.
It was possible Peters was hoping he would be caught so he could get psychiatric help, the sentence hearing was told on Wednesday.
"It was in my view a very clumsy crime," Dr Phillips said.
But he agreed with crown prosecutor, Margaret Cunneen, SC, that as the extortion attempt could have been successful, it was probably not credible that Peters wanted to get caught.
The hearing continues before Judge Peter Zahra.