Aaron Jenkins (20) murdered Stephen Whitehead when he came across his enemy asleep between two chairs at Pendle Skips in Burnley on July 25th last year.
Two weeks earlier the men had been in a fight in which both were injured as they sorted waste on a conveyor belt at the recycling plant in Balderstone Close.
When Jenkins broke into the yard on July 25th - intending to steal a motorbike – he found Mr Whitehead asleep after a night out drinking, and thought: “Payback time.”
As Mr Whitehead dozed, with his feet up and a radio playing, Jenkins crept into an office and picked up a sledgehammer.
He returned to the canteen and rained blow after blow down onto Mr Whitehead’s skull.
Mr Justice Kerr, sentencing, said: “If you had not decided to burgle the premises he might well be alive now.”
Following the attack he returned to a friend - who was waiting by the gates, and told her he’d killed someone.
The following day he instructed the teenager - who cannot be named for legal reasons - to provide him with an alibi, saying they had been together at the time of the attack.
Sentencing Jenkins for life, with a minimum term of 17 years, Mr Justice Kerr said: “You brutally bludgeoned Mr Whitehead to death with a sledgehammer while he slept.
“You did this because you had a score to settle with him. You had fought with him two weeks earlier and received an injury. As you admitted, you decided it was payback time.
“You struck him several times on the head. He did not stand a chance.
“It was a horrific attack on a defenceless man. Your cruelty has taken from his 24 year old daughter the father she loved.
“His five brothers and sisters have lost their beloved brother. Their appalling suffering continues and will continue.
“I am not sure you intended to kill Mr Whitehead. If you had been a cool-headed and mature man I would have had no doubt about the intention to kill just because of the nature of the blows struck and the weapon used.
“But you were a very young man of low intelligence and with a significant learning disability.”
Mr Whitehead was discovered slumped between the chairs by work colleagues when they arrived at work at around 7am on July 27th.
Emergency services were called to the scene where Mr Whitehead was declared dead.
In a victim statement, members of Mr Whitehead’s family said: “He was part of our family and was a hard-working man who liked a drink.
“He lived the way he did causing no harm to anyone. We are devastated by the sudden and violent nature of his death.”
Jenkins, of Devonshire Road, Burnley, admitted he had killed Mr Whitehead but denied murder on the grounds of diminished responsibility.
The court heard he has the mental functioning of an eight or nine year old child.
A teenager was also jailed for eight months for attempting to pervert the course of justice by providing a false alibi to Jenkins