Murder-victim Joanna Yeates could have been strangled with her own sock which her killer might have kept as a trophy.
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.
Detective 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.
Ms Yeates was found dead in Longwood Lane, Failand, North Somerset, south-west England, wearing just one sock. She was not wearing her coat or boots either but those items were recovered from her flat in Bristol.
Det Ch Jones said: "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."
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 Ms Yeates was strangled with it.
Ms Yeates's landlord, retired Clifton College teacher Chris Jefferies (65), was arrested on suspicion of her murder but freed on bail after three days of questioning.