A teenager was hacked to death by three friends who attacked him with large scythes, a court heard.
Terry Lee Hurst had been camping overnight
Terry Lee Hurst was targeted by the three during a camping trip to Broomhead Reservoir on the outskirts of Sheffield in July 2004.
A 17-year-old youth pleaded guilty to Terry's murder on Tuesday. Another 17-year-old and 16-year-old girl admitted the killing on Monday.
At Sheffield Crown Court the judge ordered reports before sentencing them.
Legal restrictions mean none of the defendants can be named.
After the hearing Det Insp Tom Whiteley of South Yorkshire Police said investigators had not established a motive for the killing.
"I cannot visualise what goes through a person's mind to commit a protracted attack of such a ferocious nature," he said.
"The injuries that were inflicted on this young man were horrific to say the least. In fact, the worst I have ever seen."
Mr Hurst sustained more than 60 wounds. The only weapons found at the scene were two agricultural scythes.
These had been taken from the nearby village graveyard at Bolderstone church where the grass was being cut down.
Mr Whiteley said interviews with Terry's killers failed to establish any real motives for such a vicious attack.
The victim was originally form the Shiregreen area of Sheffield but had moved to Penistone, near Barnsley.
The officer said: "He was a good lad. He has certainly not been in trouble with the police before.
"He was known locally as a good samaritan. He would help anyone out and would never cause any particular problems for anyone."
Trial judge Mr Justice Smith ordered reports on the defendants and adjourned the case until a future date.
He said it was a "desperately sad case".