The DNA of a suspected murderer who is also accused of raping a 16-year-old girl was found on a sample taken from her underwear, a court has heard.

Donald Robertson denies the kidnap and rape of the girl, who cannot be named for legal reasons, on July 16, 1981.

He is also accused of killing 26-year-old Shani Warren, whose body was found bound and gagged in Taplow Lake in 1987.

Robertson, now aged 66, who was not in court, denies the false imprisonment, indecent assault and murder of Ms Warren between April 16 and 19 1987.

His alleged rape of the 16-year-old occurred less than four miles away from where Ms Warren’s body was found, the court previously heard.

On the third day of his trial at Reading Crown Court, jurors heard from forensic scientist Stephen Paddock, who gave evidence relating to the alleged offences against the 16-year-old.

He presented findings from a team of forensic scientists, who used modern DNA analysis methods to look anew at samples taken in 1981.

These included extracts taken from the alleged victim’s vaginal swabs and from tapings used to collect DNA from her underwear.

Tests of one taping-derived sample found traces of three people’s DNA, including Robertson’s, the court heard.

Mr Paddock said this could have been from them being contaminated in a lab.

The court also heard how clothes can get DNA traces by other people handling them prior to an alleged offence.

However, prosecutor John Price QC said the result showed “an apparent major contribution of DNA which matched the DNA reference sample from Mr Robertson”.

Mr Paddock confirmed this appeared to be the case, later telling the court: “In my opinion, the DNA matching Robertson has originated from semen.”

He also told jurors it was a “billion times” more likely the three DNA sources came from Robertson and two unknown individuals, rather than three unknown individuals and not the defendant.

The vaginal swab tests found traces of sperm but the readings were too weak to give any results.

The court previously heard Robertson was questioned by police in 1981 in relation to his alleged rape of the 16-year-old, but he denied the offence at the time and was released.

Robertson also has convictions for raping two girls aged 14 and 17 in separate incidents, Reading Crown Court has heard earlier in the trial.

He was also convicted of burglary with intent to commit rape and kidnap following an incident in Slough in April 1990.

He was charged in October 2021 over Ms Warren’s death.

Prosecutor John Price QC previously told jurors he believes there are similarities between the defendant’s confirmed and alleged crimes.

Mr Justice Wall earlier told the court it is Robertson’s own choice not to attend, that he has a right to make such a choice and it should not be held against him.

The trial continues.