The Court of Appeal has ordered an investigation into fresh evidence which could help clear a deputy head teacher jailed for killing his foster daughter.
Jenkins was given the right to appeal for a second time last year
Sion Jenkins, from Hastings, was jailed for life in 1998 for the murder of 13-year-old Billie-Jo Jenkins.
Three appeal judges have been told a mentally ill man in the area at the time had shown signs of a fixation with pushing pieces of plastic up his nose.
A pathologist found Billie-Jo had part of a bin liner pushed up her nostril.
Jenkins was convicted at Lewes Crown Court of the murder of Billie-Jo who was battered to death with a metal tent spike in the back garden of their family home in Lower Park Road, Hastings, in February 1997.
An appeal by Jenkins, who was deputy head at William Parker School in Hastings, was dismissed in 1999.
Jenkins, whose family are from Aberystwyth, west Wales, was given leave to appeal again in May last year after a review by the Criminal Cases Review Commission (CCRC).
Billie-Jo was beaten to death with a metal tent spike at her home
The appeal will not be heard before 1 July.
In a preliminary hearing on Thursday, judges at the Court of Appeal in London were told of the man who had shown signs of a fixation with pushing pieces of plastic bag up his nose.
They asked the CCRC to inquire into whether the man "exhibited any unusual behaviour in relation to plastic bags or sheets or other plastic objects", while in police custody or subsequently in a secure mental unit.
Clare Montgomery QC, representing Jenkins, said the plastic found in Billie-Jo's nostril was "a singular and striking feature of the murder".
'Lurking out there'
She told the court it did not fit in with the prosecution case that Jenkins killed his foster daughter quickly in a fit of rage.
Crown counsel Richard Camden Pratt QC opposed the call for a fresh inquiry.
He said the only evidence against the mentally ill man was that he was in the vicinity at the time, as were hundreds of other people.
He told the court the suggestion was that his mental illness made him more likely to kill.
Lord Justice Kay said the public had a legitimate interest in seeing justice done and the court could not "brush aside" the possibility that other evidence may be "lurking out there".
At the full appeal, the court will also hear discussions as to why the two daughters who were with Jenkins on the day of the death were not called to give evidence.
They now live in Australia with their mother, who has divorced Jenkins, and are expected to fly to the UK to give evidence in the appeal.