A teenager was stabbed well in excess of 100 times in a remote woodland spot, a court has heard.
Alex Davies, 18, was killed on Parbold Hill in Lancashire, where he had agreed a rendezvous with Brian Healless, also 18.
The pair, who had never met before, exchanged mobile phone messages to arrange the location but more than a hour later Healless was seen on CCTV cycling away from Parbold and carrying Mr Davies's rucksack, Preston Crown Court was told.
The prosecution say Healless took a kitchen knife to the scene, where he attacked Mr Davies on the afternoon of April 28, concealed his body and then "simply rode off" on his mountain bike to his home in Chorley.
Opening the case on Tuesday, David McLachlan QC told jurors that Mr Davies, from Skelmersdale, was openly gay and the defendant had been in contact with him and other gay men.
On May 1, a local gamekeeper was doing his daily rounds on Parbold Hill when he reported seeing an arm under a pile of broken conifers.
Police found a male body covered with branches, and the victim's face was covered by a black dressing gown.
Clothing and personal documents belonging to Mr Davies were also discovered nearby, along with a black- handled knife which was secreted in the ground, the court heard.
Mr Davies was identified and a post-mortem examination showed the cause of death was multiple stab wounds and asphyxiation.
It was also noted that he had been beaten around the head and appeared to have been dragged through the mud face down.
Healless was arrested on May 3 and a search of his bedroom uncovered the victim's headphones, wallet and spare phone.
Mr McLachlan told the jury that the defendant accepts that he killed Mr Davies.
He said: "We may never know why he did it but the painstaking police investigation means that the finger points fairly and squarely at Brian Healless.
"And the police were right to point the finger at him as he now admits to the unlawful killing of Alex Davies.
"To be clear, the issue for you will be whether this is a case of murder or a case of manslaughter by reason of diminished responsibility.
"You will have to determine whether or not Brian Healless was suffering from an abnormality of mental functioning at the time of the killing which substantially impaired his ability to understand the nature of his conduct or to form a rational judgment or to exercise self-control."
He said the jury would hear evidence from psychiatrists who had examined the defendant.
Healless, formerly of Rylands Road, Chorley, denies murder.