UPDATE 3:34PM DETECTIVE Superintendent Luke Moore said police were treating the Mosman bomb incident as a "serious and complex investigation" and an unusual crime.

He said police were conducting extensive forensic examination at the family home on Burrawong Avenue.



"We have some initial lines of inquiry that we are following up," he said.



"There's a lot of resources involved in this investigation."



Supt Moore confirmed there was a letter of demand attached to the device that was believed to be a bomb.



"It was an elaborate device certainly made to look as though it was potentially explosive," he said.



"We are treating this as an attempted extortion."



Supt Moore said police did not have a full description of the offender, but there was "no doubt" police were looking for a suspect.



Supt Moore said he could not reveal what was in the demand letter but there was no information to suggest that this was linked to any other crime.



"We don't have a description but we do believe he was wearing a balaclava," he said.



The man was in the house for a short time, he said.



He said "Madeline was the victim" when questioned whether she may have been involved in the hoax.



He said he could not estimate what the operation on Wednesday would have cost the state.



Madeline and several other people will be interviewed in the next few days.



Most of the residents who were evacuated from the street have returned to their homes but forensics were still working at the street, Supt Moore said.

"A very, very elaborate hoax as it turned out," New South Wales Police Assistant Commissioner Mark Murdoch said after police released Madeleine Pulver from the device following a delicate 10-hour operation last night.



"But it was made and certainly gave the appearance of a legitimate improvised explosive device," he told the media outside Madeleine's home at the Sydney harbourside suburb of Mosman.



"We had to treat it seriously until we could prove otherwise and that's exactly what we did and that's why it took so long.



"'It was affixed to her by a chain or something similar, which eventually took us a fair while to remove ... and that added to the trauma that Madelaine experienced and prolonged," Murdoch said.



He said the bomb was "very elaborate, very sophisticated" and it took "the best we have in our NSW police force bomb technicians ... it took their best to free the girl and make her safe after 10 hours".

LATEST PHOTOS, VIDEO FROM THE SCENE



Mr Murdoch said detectives are at a loss as to why Madeleine and her family were targeted.



The unprecedented incident has shaken the prestigious North Shore community, which locals described as "quite private".



"Of course we are shocked," one neighbour said.



Mr Murdoch this morning gave an insight into how Madeline was coping as experts frantically worked on the safest ways to defuse the bomb.



"From what Madeline told police when they first arrived, that caused us some level of significant concern," Mr Murdoch told 2GB's Alan Jones.



"She was seated in the house ... she was clearly upset".

media_camera The scene ... Police Forensic officers at the Burrawong Ave, Mosman home where an 18 year old girl had a bomb type device attached to her body. Picture: Attila Szilvasi

Mr Murdoch said a young female officer sat with Madeline "talking to her and keeping her calm".



He said two hours in, the female officer was replaced by two negotiators and two technicians "who worked in relays to free her".

Burrawong Ave, Mosman remains a hive of police activity this morning as detectives continue to scour the Pulver mansion.

The intersection of Kardinia Rd and Barrawong Ave remains closed to traffic and police continue to conduct their investigation.



The Pulver family have not returned to the house since Madeline was freed from the bomb shortly after 12.30am and taken to hospital for a check-up.

Forensics officers left the the hospital overnight with evidence bags, possibly containing victim's clothing and other remained outside the home fingerprinting a white Ford station wagon.

media_camera Freed .. Police follow an ambulance containing the Mosman girl involved in a bomb threat extortion to RNS Hospital after the incident was over. Picture: Bill Hearne

Bomb specialists were able to release Madeleine from the collar bomb just after midnight after getting expert advice from the Australian Federal Police bomb centre and the British military.

The device, which police were unsure was explosive, was still intact and will undergo thorough forensic examination.

media_camera An ambulance with Madeleine Pulver onboard rushes to RNS Hospital after the bomb was diffused. Picture: Bill Hearne

Assistant Commissioner Mark Murdoch said Madeleine's parents William and Belinda Pulver - one of Sydney's wealthiest families - were "immensely relieved" and that the girl was safe.Mr Murdoch described it as a "very elaborate device" and police were continuing to investigate an elaborate extortion but would not reveal details of the threat or demands.

During the 10-hour ordeal at the family mansion in Burrawong Ave, Mosman, Madeleine was fed, given water, kept warm and was in the company of specialist police officers while her parents were kept away.

Mr Murdoch said she was in a "uncomfortable position" during the "unusual incident" and was taken to hospital for assessment early today.

"She has disclosed a lot of information to police. That information will now be acted upon," Mr Murdoch said.

"The family are at a loss to explain this. You would hardly think someone would go to this much trouble if there wasn't a motive behind it.

"There were some instructions left by the offender at the scene last afternoon and those instructions will provide us with further lines for inquiry.



"Those instructions also limited us somewhat last night in how quickly we could proceed.



"Certainly the instructions were precise, they were such that led us to believe that we were dealing with a very serious and legitimate threat."

He was not aware of "anything like this happening in NSW or this country before".

He said the police have not had contact with who is responsible but "want to get our hands on them pretty smartly".

media_camera Police forensic officers at the Burrawong Ave, Mosman home. Picture: Bill Hearne

Experts from the NSW Bomb Squad spent a number of hours inside the house examining the device while it remained secured around the terrified teenager's neck.

Officers arrived and immediately called for specialised help after realising the gravity of the situation.

Experts from the NSW Bomb Squad spent a number of hours inside the house examining the device while it remained secured around the terrified teenager's neck.

X-rays were taken of the device to allow a more detailed check before any attempt to defuse it was made.

Mr Murdoch said police were speaking with a number of agencies, "not internationally, but within Australia, the AFP in particular" but that the AFP were "making inquiries internationally".

Roy Ramm, a former commander of specialist operations with Scotland Yard's hostage response team, said the incident had received significant media attention in Britain.



He said the police who went to Ms Pulver's aid would have faced an extremely complex and stressful situation, including the prospect of the device being remotely detonated, or set off by a trembler switch.



He said police would have had to keep her extremely still - trembler switches activate bombs when devices are tilted beyond a certain angle.



"They primarily would have been concerned about keeping this young woman calm ... to sit extremely still," he told ABC Radio.



Mr Ramm said trembler switches were typically attached to car bombs, used by the likes of the Provisional IRA and other terror groups.



He said experts responding to the drama would have had a range of technology at their disposal, including airport-style swabs that could detect explosives.



But response teams would not have wanted to take any risk with Ms Pulver's life, nor their own.



He said the most important piece of evidence police had was the device itself.



"There'll be a really detailed forensic examination of this device to see if there's any DNA on it, to see if it might match DNA held in any databases," Mr Ramm said.



If no match was found, any harvested DNA would be held in the hope of matching it to a future suspect.



Mr Ramm said police would also carefully look at the woman's movements, including CCTV footage, to see if she may have been followed, and any abnormal contact with the family.

The Daily Telegraphunderstands the extortionist, clad in a balaclava, entered the house shortly after 2pm and took Madeleine hostage.

It is believed he ordered her to a room towards the front of the house and directed her to sit down while he strapped a device around her neck.

While he was rigging up the explosive, the man ordered a terrified Madeleine to be limited in what she told police, or else he would remotely detonate the bomb.

It is understood the girl was told she could ring police to alert them to her predicament, but she must not give too much detail about him or their conversation. The man told Madeleine he would be able to hear her and what she told police, indicating he had planted listening devices within the house. With the bomb secured, he then left.

After Madeleine's family contacted police, saying their daughter needed help, a general duties police car with two officers went to the scene.



"What they saw was a very distressed young lady with what we believed to be at the time an improvised explosive device attached to her body," Mr Murdoch told Fairfax radio.

The teenager did not move from a room at the front of the house during the ordeal last night. Asked whether the girl could move away from the bomb, Mr Murdoch said: "No, she can't get away from it."

Madeleine, who celebrated her 18th birthday last month, is in her final year at the prestigious Wenona School in North Sydney.

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Originally published as Cops: bomb was an elaborate hoax