Rikki Neave was strangled by an older boy with a “morbid fantasy” and “sexual interest” in small children, a court has heard.

James Watson is on trial at the Old Bailey accused of murdering the six-year-old in Peterborough woods when he was 13.

Over 20 years later, Watson’s DNA was allegedly found on Rikki’s clothes, which had been discarded in a nearby wheelie bin.

On Wednesday, prosecutor John Price QC set out a detailed version of events pieced together from evidence in the case.

He told jurors Watson and Rikki were seen walking from the city’s Welland Estate on November 28 1994.

He said: “It was a sunny late autumn day and they were going to a place both of them knew well and both had visited many times before, at least during daylight – they were going to the woods.

“Some time after the two boys arrived in the wood, from behind and without warning James Watson ambushed Rikki Neave and strangled him to death using a ligature, whether it was the collar of the jacket Rikki was wearing or something applied on the collar.

“Rikki was wearing the jacket when he died and it was still zipped up because the zip left a telltale mark on his neck.

“James Watson then stripped the child’s body. He had an abiding sexual interest in small children which he had already acted on in the previous year, an interest reinforced with a morbid fantasy about the death of a child known to have been on his mind as recently as three days earlier.”

Mr Price said one of Rikki’s shirt buttons came off and was placed on a nearby leaf as Watson “did whatever he was doing”.

Watson then posed Rikki’s body “much as he did with a dead bird” he killed months later, jurors heard.

He then took Rikki’s clothes and dumped them in the bin, the court was told.

Afterwards, Watson became “fascinated by the consequences of his own act”, copying newspaper stories on Rikki’s death, Mr Price said.

But when he talked to teachers he did not reveal he had been with Rikki that day, only mentioning it to police when they called days later, the court was told.

His account was not questioned or challenged for over two decades, during which time Watson acquired a “considerable amount of forensic experience”, Mr Price said.

So before police told him about the DNA link to Rikki’s clothes, he prepared an explanation – that he had picked him up to look through a hole in a fence, Mr Price suggested.

The prosecutor said: “He would tell them how, all these years later, the memory of the little boy peering through the hole in the fence still made him chuckle when it came to his mind.”

That was, Mr Price said, Watson’s “really big mistake because it never occurred to him all these years later it would be possible to conclusively prove that the high fence was not there” on the day Rikki was murdered.

Watson, now 40, of no fixed abode, denies murder. The trial continues.