TWO teenagers who wanted to experience murder told police it "felt right" to strangle a friend and bury her body in a shallow grave beneath her West Australian home.

The 17-year-old girls, who cannot be named due to their age, today faced a sentencing hearing in Perth Children's Court after pleading guilty to murdering Eliza Jane Davis in the small coal mining town of Collie on June 18, 2006.

As the girls sat stony-faced in court today, Prosecutor Simon Stone said they had confessed that after partying with Eliza on the Saturday night they decided to kill her.

"Sunday morning me and (her) woke up, and we were just talking, and for some reason we just decided to kill her," one of the girls told police in her interview.

"We just did it because we felt like it, it is hard to explain," the other girl said.

"I knew we had wanted to kill someone before.

"We knew it was wrong, but it didn't feel wrong at all, it just felt right."

The girls planned their attack and changed into old clothes.

One of them snuck up behind Eliza as she was reading, wrapped speaker wire twice around her throat and quickly tightened it as the other held her down, trying to press a chemical soaked cloth into her mouth.

"She started not being able to get her breath, and we just kept going," one of the girls said.

"She was just yelling at us 'What the f**k, what are you doing' .. 'Oh you freaks, what's wrong with you psychos."

Mr Stone said they chose to strangle Eliza because one of them had to return to Perth that afternoon and they wanted a quick and "non-messy" killing.

"As our friend, we did not really want her to suffer," one told police.

"We didn't really expect to get away with it.

"We were willing to take the risk."

The girls regretted the fuss the killing caused but neither felt remorse for their dead friend, Mr Stone said.

"If she had died another way it probably would have bothered me ... but it just did not," one girl said.

The girls reported Eliza missing after they buried her and pretended to help her family look for the dead girl.

The girls turned themselves in several days later, walking into separate police stations and directing authorities to where they buried her body.

Mr Stone told the court the girls had no remorse and were holding back on the reason behind their cold-blooded, premeditated, sadistic killing.

"It is a mystery your honour, what happened."

He said the girls had discussed killing someone else and one had prepared for homicide by killing two kittens.

"Whilst together (they) will continue to pose some risk to others in custody."

Mr Stone called for sentences of life in prison.

The hearing continues tomorrow.