Rikki was killed in a “swiftly executed” attack from behind in woods near his Peterborough home in November 1994, the Old Bailey heard.
Afterwards, he was stripped naked and deliberately posed in a star shape, jurors were told.
His clothes were later discovered dumped in a wheelie bin nearby.
More than 20 years later, James Watson, who was aged 13 at the time, was charged with murdering Rikki after his DNA was allegedly identified on the trousers.
On Thursday, jurors in his trial were shown pictures of Rikki’s clothes, before the original pathologist in the case gave evidence.
Describing the crime scene, Dr Nat Cary told jurors: “I entered an area of scrubland adjacent to the road.
“There I was shown the body of a completely naked young male lying on his back with his arms and legs symmetrically spread-eagled.
“There was a mark clearly visible on the neck. There was petechial haemorrhage to the eyes and the face.”
He said rigor mortis had set in and there was mud on Rikki’s face, abdomen, knees and feet.
He noted some scars to the body and minor bruises and grazes to the head.
There was a ligature mark on the neck in a “repetitive linear” pattern, possibly from a zip fastener, he said.
The court heard he had made the observation before seeing Rikki’s jacket.
Dr Cary suggested Rikki was strangled by grabbing his clothes in a “twisting action” from behind.
He said it was a “swiftly executed” single attack and he was placed in the position in which he was found soon after death.
After seeing the jacket, Dr Cary said he was “more certain” it was used to strangle him, but added his finding was not absolute.
The court has heard that Rikki’s mother, Ruth Neave, was initially wrongly accused of his murder, and acquitted after a trial.
The DNA evidence against Watson emerged in 2015 after a cold case review was launched, the jury has heard.
Watson, of no fixed address, has denied murder and the trial continues.