Teens to serve 15 years for 'gruesome' murder of friend

Two teenage girls have been sentenced to life imprisonment in Western Australia for murdering their 15-year-old friend who they then buried in a shallow grave in the south-west town of Collie.

The two girls, who are now 17, pleaded guilty to killing their friend, 15-year-old Eliza Jane Davis in June last year.

They covered her mouth with a chemical-soaked rag and strangled her with a piece of wire.

President of the Perth Children's Court, Denis Reynolds, said the offence they committed was gruesome and merciless in the extreme and showed a gross disregard for human life.

But because of their age, the pair will eligible for parole after serving a minimum of 15 years.

Outside, Eliza Davis' grandfather expressed his outrage at the sentence.

"They'll be free running around in 15 years and I've lost a grand-daughter," he said.

"I'll never get her back."

Their sentence will be backdated until June last year when they were taken into custody.