Russell Bishop is on trial for the murders of nine-year-olds Karen Hadaway and Nicola Fellows

A cold case expert has told jurors of a one-in-a-billion DNA match to alleged killer Russell Bishop on the arm of two girls found dead in woodland 32 years ago.

Russell Bishop, 52, is on trial at the Old Bailey charged with the murders of nine-year-olds Karen Hadaway and Nicola Fellows.

The girls were sexually assaulted and strangled in Wild Park in Brighton in October 1986.

Bishop was acquitted of the murders in 1987, but ordered to face a fresh trial in light of new evidence from advances in DNA testing.

Forensic scientist Roy Green tested 14 areas from a taping from Karen's left forearm, taken at the time of her post mortem examination in 1986.

He said the areas were identified as possibly containing skin flakes or other organic material.

Nicola Fellows (left) and Karen Hadaway (right) were found dead after going out to play in 1986

The girls were found in this den in Wild Park, Brighton, their bodies hidden by undergrowth

On his results, Mr Green said: 'The result of the DNA-17 analysis showed a mixture of DNA from at least two people.

'The majority of the DNA was an incomplete profile matching that of Russell Bishop. Most of the remaining components also contained the DNA of Karen Hadaway.

'There were also three additional components other than from Russell Bishop and Karen Hadaway.'

Tapings from a blue Pinto sweatshirt found discarded on Bishop's route home were also tested for DNA.

Mr Green told jurors the results found DNA 'in excess of one billion times more likely' to belong to the defendant and an unknown person than two unknown people.

On the evidence from the arm, Mr Green said he looked at two propositions, the first that the DNA was from Karen, Bishop and an unknown person, and secondly that it was from Karen and two unknown people.

He said: 'A statistical evaluation of the result was performed, as a result of which it was estimated that the DNA findings would be approximately one billion times more likely if proposition one were true rather than proposition two were true.'

Bishop was put on trial for a second time after a blue jumper he is said to have been wearing on the day of the killings 'gave up its secrets' under inspection using modern DNA techniques

He said there was 'extremely strong support' for the proposition that Bishop's DNA was on Karen's arm and the Pinto sweatshirt.

There was 'moderate support' for the assertion that four human hairs retrieved from the Pinto belonged to the defendant, he said.

Cross-examining, Joel Bennathan QC queried why only 23 fibres relating to the girls' clothes were found on the Pinto sweatshirt if it was worn during the course of an attack.

Mr Green said: 'The fibres that are transferred will fall off depending on the amount of disturbance.

'If that item was worn by the attacker at the scene it then has to be transported and then deposited at the railway station. After that it was found and turned inside out and turned the right way round and eventually bagged up as evidence. All of that can lead to the loss of fibres.'

Michelle Johnson, the mother of Karen Hadaway, has been attending the trial at the Old Bailey

The witness went on to stress the Pinto sweatshirt was made out of a very unusual type of fibre.

However, Mr Bennathan suggested it might be possible to see a regional concentration of the same clothing if it was sold in a local market.

The lawyer asked if 45 fibres associated with Bishop's home could have got on to the Pinto if a policeman took it there unpackaged.

The witness said the figure was too high for secondary transfer in that hypothetical scenario.

Bishop, formerly from Brighton, East Sussex, has denied two charges of murder.