The WA pair were not the only teenage killers convicted in recent days.

Last Friday, two 14-year-old girls were sent to jail for killing a Sydney taxi driver.

They were arrested shortly after one of them freely told a transit officer that they had killed Youbert Hormozi.

According to the 2004-05 annual report by the National Homicide Monitoring Program (NHMP), more than a third of all of females were killed without any apparent motive.

The report also said that there were only three females convicted of killing that were under the age of 19.

In the past week alone, four teenage girls have been convicted for over violent killings.