Perth man denies murdering mum, siblings

A Perth man has pleaded not guilty to murdering his mother, eight-year-old brother and 15-year-old sister.

Teancum Vernon Petersen-Crofts, 20, was charged with three counts of murder the day after his mother Michelle, 48, and brother Rua were found dead inside their Ellenbrook home in July last year.

His sister Bella was found injured in the backyard and died on the way to hospital.

Petersen-Crofts faced Stirling Gardens Magistrates Court on Wednesday via video link from a psychiatric facility and will appear in the Western Australia Supreme Court on March 9.

At his first court appearance, Petersen-Crofts rambled to the magistrate about his "mamma" and "painting a picture of Jesus".

He also told a security guard beside him that he looked "like a serial killer".

Just after the murders, a senior homicide squad officer said it was "potentially the most horrific crime scene" he had seen.