A teenage relative of backpacker murderer Ivan Milat boasted to friends a day after killing a 17-year-old boy with an axe: ''You know me, you know my family ... I did what they do."

''You know me, you know my family ... I did what they do,'' he told a friend according to court papers before Campbelltown Children's Court.

Ivan Milat ... the convicted backpacker killer is a relative of the teenager who pleaded guilty to murder. Credit:Adam Pretty

Documents before the court today show the boy told friends the next day: ''I killed somebody last night''.

''At one stage, the axe got stuck, so I had to kick the back of his head to get it loose.''