Man Beheaded, Another Shot Dead in Cancun, Mexico

Mr Murdoch said instructions in a ransom note left by the intruder were "articulate and specific", leading police to believe that he knew what he was well versed in bomb-making. Miss Pulver was forced to remain in one position for ten hours after a masked intruder reportedly left a ransom note warning he would detonate the supposed bomb, which was attached to her neck by a chain, if she attempted to escape. There were also reports that the perpetrator warned Miss Pulver he had left a microphone with the bomb in order to monitor her remotely.

The motive behind the attack remained unclear last night, but police said extortion remained a major line of inquiry. Police were investigating whether the family had been the subject of threats in the past. Mr Murdoch said officers were "very keen to get their hands on" the person responsible. Mr Pulver is the chief executive of technology company Appen and the family live in £1.3 million home in Mosman, one of the most exclusive districts of Sydney. Mr Murdoch said: "The family are at a loss to explain this. You would hardly think that someone would go to this much trouble if there wasn't a motive behind it."

Miss Pulver, who is a pupil at the private Wenona High School, was said to be shocked but physically unharmed in the incident. She was released from hospital during the morning and was staying with her family in a hotel while forensic police combed their home for clues. Mr Murdoch said: "She held up remarkably well.

"She's good, she's been kept in an uncomfortable position for more than 10 hours but now she is with mum and dad which is exactly the right place for her. A trip to hospital is on the agenda, she will be checked over by doctors."

Detectives revealed that Miss Pulver had called her father first, who alerted police. She had spoken to the intruder and Mr Murdoch said she had been able to disclose a lot of information which they were now looking to act upon.

Mr Murdoch said: "This is an unusual incident for New South Wales and Australia, I'm not aware of this happening in the country before. I've been in this job for a long time and this is a very bizarre case."

The Pulver family home is situated in one of Sydney's most elegant suburbs on the city's North Shore. Properties in the area sell for in excess of £1 million but serious crime in the area is uncommon, and many Mosman mansions have minimal security.

As the drama unfolded friends of Miss Pulver gathered near to her home to wait anxiously for news. One said: "We are here for Maddie so she knows we love her."