Detectives hunting the murderer of Joanna Yeates are grappling with the question of why the killer moved her body, it has been revealed.

A senior detective has anonymously told a national newspaper that the killer's decision to dump Jo's body three miles away from her flat was a 'massive gamble'.

He said: "Assuming the culprit was undetected carrying out the killing, why on earth did they just not leave the flat as quickly and quietly as possible?

"There would have been only a relatively slim chance someone had seen them either entering or leaving and they would not have attracted any undue suspicion."

Jo, who was born in Hampshire and went to schools in Chandler's Ford and Romsey, went missing on the evening of December 17, after walking home to her flat in the Clifton area of Bristol.

Her snow-covered body was found on Christmas Day by dog walkers in Longwood Lane, Failand and post mortem tests later revealed that she had been strangled.

It's now been claimed that officers investigating the murder are considering taking DNA samples from suspects in a similar unsolved case.

The body of Glenis Carruthers, 20, was found in 1974 just yards from where Jo lived.

Like Jo, she had been strangled, was found fully clothed and had not been sexually assaulted.

A source close to the investigation told a national newspaper: "There are a number of startling similarities between the two cases, despite the huge time gape.

"DNA testing can eliminate people very quickly and so can be very useful in narrowing the scope of the inquiry.

"As there is already a cold case review into the Carruthers murder taking place, it would be a relatively simple task to pinpoint anyone of interest and rule them out."

It's understood that detectives have recovered a small DNA sample from saliva found on Jo's body.

In another strand to the investigation, Bristol City Council has confirmed that detectives have seized plans for the huge converted Victorian mansion where Jo lived.

It's believed that officers are now inspecting the drawings to see if the murderer might have secretly stashed her body somewhere before dumping it.

Meanwhile, it's thought that the bill for the murder investigation has topped £1m, as officers work on the case round the clock.

A top criminologist, who wished to remain anonymous, said: "Obviously the huge cost of forensics on the case will already have cost a significant amount.

"The cost of the inquiry could easily have reached around £1million so far."