Joanna's killer may have used her own ski sock

Police believe the missing grey ski sock may hold the key to solving the murder of the landscape architect whose snow-covered body was found on Christmas morning.

Det Chief Inspector Phil Jones, who is leading the murder inquiry, has not ruled out the possibility the 25-year-old's killer may have used the sock to strangle her or that they kept it.

One of Miss Yeates' socks was missing when she was found dead in Longwood Lane, Failand, North Somerset. She was not wearing her coat or boots either but those items were recovered from her flat in Canynge Road, Clifton, Bristol.

Holding up a box containing a similar long, ski-style size five grey sock, Mr Jones said: "I am here this morning to talk to you about a missing sock.

"When Jo was found on Christmas Day morning in Longwood Lane, although she was fully clothed, she was not wearing her jacket, she was not wearing her boots and she was only wearing one sock.

"The jacket and the boots have been found at her home address. That would indicate that Jo had returned home.

"However, at this present time the sock has not been found. It hasn't been found at Longwood Lane and it hasn't been found at her home address.

"It is described as a light grey sock with lighter detail on the toes, heel and shin."

The detective said he was "keeping an open mind" about whether the killer or killers could be keeping the sock as some sort of trophy or whether Miss Yeates was strangled with it.

Following the appeal for the missing sock – the type bought in an outdoor shop – a man approached police outside Miss Yeates's flat and handed over a grey sock. The unnamed man, who had white hair and was wearing a black and khaki-coloured jacket, put the sock he was carrying in an evidence bag presented to him by police Police then spoke to him at the side of the property.

Following his conversation with officers by the side of the building, he left the premises via the front gate, telling waiting reporters only that he had been told not to say anything.

He was then escorted away by a police officer.

Mr Jones also confirmed that the killer or killers may have tried to put Miss Yeates's body over a wall into the quarry on Longwood Lane but instead left her on the grass verge.

"There are a number of theories about how Jo came to be in Longwood Lane and this is a possibility, yes," he said.

Mr Jones would not confirm directly that police were using a criminal profiler but said his team were receiving assistance from various expert sources.

"We continue to use all the available professional resources available to us including accredited experts who are specialists in their fields rather than generalists," he said.

"These resources have been used since the start of what was initially a missing person investigation and now a murder investigation."

Mr Jones added: "I can assure you that we will find Jo's killers."

The landscape architect was last seen walking back to the rented flat that she shared with her boyfriend Greg Reardon, 27, after going for drinks with colleagues on December 17.

She visited three shops on the way home and was filmed on CCTV buying a pizza in Tesco Express in Clifton. The receipt was discovered in her flat but no evidence of the pizza or the packaging has ever been found.

Miss Yeates was found on Christmas Day in a lane three miles from her home by a couple walking their dogs. She had been strangled.

Detectives have said there was no evidence that Miss Yeates was sexually assaulted but they have not ruled out a sexual motive for the killing.

Police said that since an advert was placed on Facebook yesterday it had been viewed nearly 250,000 times and hundreds of people have clicked through to the police's contact form.

Miss Yeates's landlord, Chris Jefferies, 65, was arrested on suspicion of her murder, but freed on bail after three days of questioning.