Sydney bomb victim Madeleine Pulver had a ransom note pinned to her signed with the name of a character from a novel that features an extortion plot.

The letter, which was fastened to the millionaire's daughter, warned: "Don't go to the cops or I will detonate. Don't cut the wires or I will detonate."

It was signed Dirk Struan – the name of a tycoon in the James Clavell novel Tai-Pan, in which a character's kids have a price put on their heads.

Sydney teenager has 'collar bomb' strapped to neck

Police found the letter after a 10-hour operation to defuse the device. The "bomb" clamped around the 18-year-old’s neck was later found to be fake, but police are treating the case as an attempted extortion.

A computer memory stick attached to it held a mystery email address.

Police hope it will help close the net on the masked intruder who burst into the £6m home of William and Belinda Pulver and their four children in Mosman, on Sydney's north shore.

He confronted Madeleine, in the kitchen when she arrived home alone about 2.30pm on Wednesday.

The balaclava-clad man fitted a replica explosive device to the teenager's neck with a chain and, before fleeing, pinned the note to her chest.

Police are also probing a possible sighting of the man as he fled from the mansion on Wednesday.

Neighbour Gai Waterhouse, one of Australia’s most prominent racehorse trainers, said she had seen a man sprinting to a waiting car – driven by a woman – just moments before police arrived.

Yesterday Police took away several computers from the Pulvers' home.

Police chief Mark Murdoch told how the attacker crept up behind Madeleine as she studied for exams.

It is thought he then ordered her into a room at the front of the house before chaining the device to her neck.

She spent hours crouching in pain, terrified the "bomb" would detonate. She had been warned she could only phone police if she promised not to describe her attacker or their conversation.

The man told her he had bugged the house and would set the bomb off if she did not follow his orders exactly.

But she phoned her mum Belinda, who alerted the police. They then swooped on the house.

Murdoch said yesterday: "There were some instructions left by the offender at the scene and those instructions will provide us with further lines for inquiry. Those instructions also limited us somewhat in how quickly we could proceed. They led us to believe that we were dealing with a very

serious and legitimate threat."

The intruder appears to identify himself with the protagonist from Clavell's 1966 novel, which is set following the British seizure of Hong Kong in 1842, and is the second novel, after Shogun, in the author's Asian saga series.

Senior police officers, including Murdoch, said they had never encountered a collar bomb or such an unusual extortion attempt in their long careers.

Murdoch praised Madeleine for her bravery, and also hailed NSW Constable Karen Lowden a hero.

Lowden, one of the first officers on the scene on Wednesday, sat with Madeleine for the first three hours of her ten-hour ordeal, despite the risk to her own life.

Lowden said of Madeleine, ''She did everything right, she was just an amazing person – the strongest girl in the world at the moment.''

Lowden, a mother to a two-year-old son said the pair spoke about Madeleine’s upcoming exams.

''There's a lot of things that we did talk about besides, (the) part of the conversation that I can't go about in great depth,'' she said.

"We also talked about her trial HSC.

''Just anything to keep her reassured … her art studies, just anything to make her feel as comfortable as she could.”

The victim’s dad, technology firm chief Bill Pulver, said he was "extraordinarily proud" of his daughter, adding that she was "in pretty good spirits" yesterday.

Earlier, Madeleine had emerged from her home saying she was well.

In the company of her parents and brothers, she was subdued, but managed to say: "I'm OK thank you."

Peter Stenning, a founding partner of risk insurance specialists Stenning Simpson, which has managed abduction payments for Australians overseas, said collar bombs were "very rare".

"In fact, I've never heard of it before in Australia," he said. "We are dealing with this constantly overseas, specifically in Columbia. There's an organisation called FARC in Columbia. And we refer to their extortion attempts as another FARC necklace."