Emma Rowley

Police were last night examining a missing teenager's computer as they worked to solve the mystery surrounding her family's burnt-out country estate.

Kirstie Foster, 15, and her parents Christopher and Jill have not been seen since their home was destroyed by a suspected arson attack at around 4am on Tuesday.

Police have searched parts of Osbaston House in Maesbrook, near Oswestry, Shropshire, but the family remain unaccounted for amid fears they died in the blaze.

The Fosters went to a friend's barbecue on Monday before returning to their home, reportedly worth £1.2m, later that evening.

It was reported yesterday that Kirstie may have been talking online to friends in the hours before the fire, which destroyed a stable block, garage and badly damaged the house itself.

A spokeswoman for West Mercia Constabulary said police were looking at Kirstie's computer.

"We are aware that Kirstie had a computer and the use of that forms part of the inquiry," she said.

Police have refused to comment on reports that bullet cartridges and pools of blood were found in the courtyard.

They said they have begun their search of the house, but warned that the process will be lengthy.

Yesterday morning teams entering the main part of the building were forced to withdraw almost immediately after debris began to fall.

They left the building for their own safety but were able to re-enter yesterday afternoon following more work to shore up the structure.

Forensic experts faced the painstaking task of sifting and examining the debris. West Mercia Police Superintendent Gary Higgins said: "We have completed a cursory search of the annexe part of the main building, which is relatively intact following the fire.

"It is not yet known if the family were in the property when the fire broke out in the early hours of Tuesday."

He said that "every possible scenario" behind the fire was being considered while investigators followed up all lines of inquiry.

Police are developing profiles for all three family members and 100 officers and support staff are working around the clock on the "unusual and complex incident".

Mr Higgins said: "I'm aware there is a lot of speculation concerning this incident. We are anxious to clarify the exact circumstances as soon as possible."

It has emerged that Mr Foster, who made his fortune developing insulation technology for oil rigs, was earlier this year branded "bereft of the basic instincts of commercial morality" by a High Court judge.

Court documents show that his company, Ulva Ltd, which had gone into liquidation, faced legal action from one of its suppliers for thousands of pounds, and also owed about £800,000 in tax.