Human rights groups last night called for the case against former deputy head Sion Jenkins to be dropped as he faced a third trial over his foster daughter's murder.

It emerged last night the cost of pursuing Jenkins over Billie-Jo Jenkins' killing could end up amounting to millions of pounds.

The police reinvestigation which led to his 11-week retrial at the Old Bailey and a hung jury on Monday cost about £400,000.

Prosecutors said they could not reveal the total when the cost of two trials, two appeals, a Criminal Cases Review Commission case and Jenkins' six years in prison were added but analysts believe the final bill will easily surpass six figures.

Eight years after the 13-year-old's killing no one has been convicted of her murder.

Jenkins was found guilty of murder at Lewes Crown Court in 1998 after the Crown insisted bloodspots found on his clothes proved he was responsible.

However, his conviction was quashed at the second attempt by appeal court judges last July after doubt was cast on crucial prosecution forensic evidence.

Father-of-four Jenkins, 47, now faces a third trial after a jury failed to reach a verdict after six days of deliberations.

During the trial they had heard the prosecution claim Jenkins struck Billie-Jo at least five times with a metal tent peg in a fit of temper.

The attack is said to have happened in three minutes at the family home in Lower Park Road, Hastings, on February 15, 1997. Jenkins' defence counsel insisted an intruder must have crept in while he visited a DIY store.

Jenkins, former headteacher-designate at William Parker School in Parkstone Road, Hastings, had his £300,000 bail renewed on Monday and awaits news of whether he will have to go through another trial.

Hazel Keirle, legal officer for the Miscarriages of Justice Organisation, said the case should now be "put to rest" following the jury's failure to reach a verdict.

She said it would be extremely difficult to find another jury whose minds had not been influenced by the high-profile case eight years on from Billie-Jo's death.

Mrs Keirle added: "If he was convicted at a third trial, he would then be in a very strong position to appeal again.

"This would result in the case possibly ending up again in the Court of Appeal and would mean the case would end up in a revolving nightmare.

"What everyone should realise is that there has to be some sort of finality. There has to come a point when you put the case to rest."

Jenkins was told on Monday he would have to live at the London house he shares with wife Christina until the end of the week, then reside at their home in Lymington, Hants.