Ronald Castree, 54, denies murdering 11-year-old Lesley Molseed by stabbing her 12 times on isolated moorland above Rishworth between October 4 and 9, 1975.

Dr Gemma Escott, who works for the Forensic Science Service, told Bradford Crown Court she examined tapings taken from inside Lesley's knickers in 1975.

She found sperm on them which provided a DNA profile that was later found to match Castree's.

She said: "The probability of obtaining the match if the semen did not originate from Ronald Castree is in the order of one in one billion."

A DVD was played to the jury demonstrating how the tapings, originally analysed for fibres, were taken in 1975.

It later showed how Dr Escott examined them for sperm in 2000 and obtained a DNA profile, Lesley's clothes having been destroyed in 1985 in accordance with police practice.

She said that although the sperm had degenerated, she was still able to obtain a positive profile which would not have altered with time.

Dr Escott ruled out the possibility of DNA from a third person being present and said procedures were in place to minimise contamination.

She said she believed whoever deposited the semen on to Lesley did so when her knickers were pulled down.

The sperm was then transferred on to the inside of the knickers when they were pulled up.

* Proceeding