A convicted sex offender on trial for the second time for the murders of two nine-year-old girls in the 1980s was play-acting when he appeared grief-stricken following the discovery of their bodies, a court has heard.

Russell Bishop, who joined a search party with his dog Misty after Nicola Fellows and Karen Hadaway went missing, described details of the position of their bodies that he could only have known as their killer, jurors were told.

The Old Bailey in London heard that Bishop was among the first at the scene of the discovery in an area known as Wild Park, part of the South Downs half a mile from the area of Brighton where the girls lived, and was told to stay back when he tried to move forward to take a closer look at the bodies.

Facebook Twitter Pinterest Russell Bishop. Photograph: Sussex Police/PA

A police officer crawled through bracken and found Karen lying across Nicola with her head in her friend’s lap. Both appeared as if they were sleeping, the court was told.

Brian Altman QC, for the prosecution, said Bishop later told a neighbour he had found the girls with three “mates” after he had obtained clothing from their parents and given it to his dog to sniff out the children.

The neighbour thought Bishop seemed grief-strickenand said he claimed that the vision of them lying across each other was a sight he would never forget.

Altman told jurors: “If he did appear to be grief-stricken then he was play-acting.”

Asked a few days after the discovery how and where the children had been found, Bishop allegedly said: “One was lying on her back and the other one was lying across the other one’s stomach. One had blood coming from the corner of her mouth.”

Altman said: “The prosecution suggests that the only way the defendant could have known the detail of the girls’ positions in relation to each other was not because he saw it at the time of finding, but quite simply because that is how he left them, having killed them.”

Bishop, who was 20 at the time and is now 52, is being retried after his 1987 acquittal for the killings of the two girls was quashed at the court of appeal in light of new evidence following advances in DNA testing. He denies two charges of murder.

Less than three years after the 1987 acquittal, Bishop kidnapped, indecently assaulted and tried to kill a seven-year-old girl in Brighton. He was found guilty of that attack in 1990.

The Old Bailey jury has heard of “striking and obvious” similarities between the deaths of Nicola and Karen and the sex attack on the other child three years later.

The trial has heard that a light blue sweatshirt discarded in the area near where Nicola and Karen died had “given up its secrets” following advances in DNA testing. Altman said the sweatshirt, which Bishop denied owning, was not only linked to him and his home environment but also provided several scientific links to the girls, supporting the prosecution case.

The trial continues.