A Perth man has been found not guilty by reason of unsoundness of mind of murdering his mother, sister and half-brother in their Ellenbrook home.

Teancum Petersen-Crofts, now 21, had pleaded not guilty to stabbing to death 48-year-old Michelle Petersen, 15-year-old Bella and eight-year-old Rua, in their Brixton Crescent home in the north-eastern suburb of Ellenbrook in the early hours of the morning on July 15, 2018.

Delivering his judgment on Monday, Chief Justice Peter Quinlan said he was satisfied Petersen-Crofts killed all three of his family members and at the time he was not criminally responsible on account of unsoundness of mind.

“In particular I find you were suffering from schizophrenia,” Justice Quinlan told the Supreme Court.

People were left in shock after the Ellenbrook tragedy. Photo: AAP

He said Petersen-Crofts suffered from the illness since he was 14 or 15 years old and was suffering from the symptoms at the time of the murders.

Petersen-Crofts sat in the dock with a support worker by his side, while members of his family sat at the back of the court.

His 48-year-old mother Michelle Petersen suffered 54 wounds, while his sister Bella and half-brother Rua were stabbed more than 40 times.

Petersen-Crofts had pleaded not guilty by reason of unsoundness of mind.

The trial only heard evidence about his mental state.

More to come.

–ABC