Parents call for help to find killer who probably knew murdered daughter Jo

David and Teresa Yeates urged anybody who knew somebody who had reacted strangely to the murder to come forward and end their family's pain.

"It would appear that the nation is shocked and appalled by what has happened to our daughter," they said. "Do you know someone who has been, somehow, justifying her being killed?

"Please help us identify the killer. Jo was probably acquainted with her killer."

Mr Yeates, 63, and his wife, 58, said they spent much of their time thinking how their daughter could have ended up dead by the side of a country lane.

Miss Yeates was last seen on December 17 as she made her way home from a Christmas drink with work colleagues at a pub in Bristol city centre to her flat in Canynge Road, Clifton. The 25-year-old's snow-covered body was found by dog walkers three miles away on Christmas morning.

Officers are set to film a reconstruction of her last walk home which will be aired on the BBC's Crimewatch later this month.

And police have obtained Land Registry plans which show how Miss Yeates's killer could have entered and left her flat without being seen by her neighbours. Detectives have established she did return home on the night she disappeared but they are still investigating how her body came to be dumped in the lay-by.

Reading a statement, her parents added: "Nearly the whole country has been moved by the tragic events surrounding Jo's murder. Many of us are 'armchair detectives', but if this activity triggers anything please come forward.

"If you do know something and you do not come forward you are consciously hampering the apprehension of Jo's killer(s) and the perpetrator(s) is still free. You will also be prolonging the torment of Jo's family and friends."

Mr and Mrs Yeates were joined by Miss Yeates's brother Chris, 28, and boyfriend Greg Reardon, 27.

The parents continued: "Do you know anyone that hasn't been shocked or disturbed? Has anyone you know had an unusual or inexplicable reaction?

"Was their behaviour unusual on the weekend of 17/18/19th December, or throughout the past three weeks?

"Do you know someone who has been behaving out of character either by actions, or what is said – or not said? Do you know someone who has inexplicably become reclusive, quiet or vocal?"