Three years' detention for WA killer teen

A West Australian teenager, who in an alcohol-fuelled rage killed his mother's ex-partner with a 15kg brick slab, has been sentenced to three years' detention.

"This was a brutal manslaughter explained but not excused by your intoxication," Justice John McKechnie told the 17-year-old, known only as JLT.

He threw the slab of paving at the head of the 51-year-old man in Geraldton, in the state's Mid West region, in June.

The victim was struck at least three times and at least one blow occurred when the man was already on the ground, causing extensive injuries, the judge said.

The youth stood trial for murder but was found guilty of the lesser charge of manslaughter.

The WA Supreme Court heard on Tuesday the pair had been drinking with others before the teenager was stabbed in the hand with a knife. He then threw the brick at the victim's head.

Justice McKechnie said they had been friendly before the altercation.

He said the victim was killed "without good reason" because the teenager was drunk but accepted that he was remorseful and was a low risk of reoffending.

Justice McKechnie warned JLT to stay away from alcohol.

"We now know what you are capable of (when drunk)," he said.

The judge said the sentence was significantly less than if JLT had been an adult.

But he said no sentence could measure the life of another person.

Justice McKechnie told JLT he had robbed a man of his life and caused grief and sorrow to those who knew the victim.

The court heard the teenager had no positive male role models and little education but had made good progress since being in custody.

He must serve at least 18 months behind bars before he can be released.

He turns 18 in May and authorities will have to make an application if they want him transferred to an adult prison.