A 52-year-old man has been given a life jail term for murdering an elderly Mandurah woman after she disturbed him trying to break into her home.

Colin Peter Casey used a tomahawk to hit 73-year-old Margaret Bromley from behind in October 2010.

He struck her in the head twice and left her to die on her patio.

He then fled the scene after stealing jewellery.

The Supreme Court was told that years earlier Casey lived next door to Mrs Bromley and he knew her husband had died and that she lived alone.

The court heard Casey was an amphetamine user who had been trying to rob his victim to get money for drugs.

His lawyer said he was in a state of desperation and exhaustion when he committed the murder.

He told the court his client panicked when Mrs Bromley threatened to call police.

Justice Eric Heenan sentenced Casey to life imprisonment but said he would not determine what minimum term Casey would receive until next month.

Members of Mrs Bromley's family were in court for the hearing.

Detective Senior Sergeant, Cameron Western, says they hope a substantial minimum term is imposed when Casey's sentencing is completed.

"What they would like to see is a sentence that impacts on people or drug related crime in general," he said.

"That's certainly a bit of a focus for them."