Mandurah teen jailed for 15 years after 'heinous' home invasion seriously injures three people

A Mandurah teenager who smashed his way into a Barragup home on Australia Day before inflicting serious injuries on three people has been sentenced to 15 years in prison.

Klay Thompson, 18, appeared in the Perth District Court on September 3 and pleaded guilty to committing an aggravated home burglary and two counts of grievous bodily harm.

State prosecutor Elisabeth Noonan told the court Thompson, along with three-to-four unknown assailants, forced his way into a home on Tranquil Retreat about 10.15pm on January 26.

The offenders were wearing face masks to hide their identity and were armed with weapons, including a handgun, rifle and golf club.

The home's inhabitants, a 47-year-old man, 18-year-old man and 17-year-old girl, were attacked by Thompson and the intruders.

The 47-year-old homeowner suffered a fractured skull, cheek bones and arm, while the 18-year-old was left with a broken nose and eye socket.

The 17-year-old, whom Ms Noonan said was Thompson's former girlfriend, sustained a broken arm and bruised right eye.

During the altercation, which lasted between five and 10 minutes, the 18-year-old man dislodged Thompson's mask, unveiling his identity.

He was arrested by police on January 28.

Thompson's lawyer Steven Shadgett said his client had "made some very terrible decisions" and had a problem with drugs in the past.

Judge Alan Troy said the minimum sentence for occasioning grievous bodily harm during an aggravated home burglary was 15 years and labelled Thompson's behaviour "appalling".

"The heinous nature of your offending is very apparent," he said.

"What happened that night is by far the most serious act of violent criminality that I have dealt with in three-and-a-half years as a judge."

Judge Troy sentenced Thompson to 15 years in prison, backdated to January 28 and made him eligible for parole.

The offenders that accompanied Thompson have not been apprehended.