Her brother heard her cry out and then the call cut off. He immediately phoned his nephews and asked them to get home to check on their mother. He knew something was badly wrong.

Her son Adam was two minutes away and immediately rushed to her Heidelberg West house where he found Xochil Quetzal O'Neill in the front bedroom standing over Ms Steenbeek, armed with a decorative Samoan paddle he had picked up inside.

O'Neill lived across the street, but they didn't know each other.

He was ranting about God and appeared to be in a psychosis. Adam told him the police were coming and to leave now. He asked if his mother was alright and O'Neill told him yes but didn't leave.

Adam went inside, taking the family dog with him and confronted O'Neill, who tried to hit Adam with the paddle. O'Neill was dragged outside by the dog and Adam struck him with the bat to incapacitate him while he checked on Ms Steenbeek.

She was in the foetal position and had suffered fatal blows to the head and upper back.

The 61-year-old yoga and pilates teacher, who had begun cancer treatment earlier that month, died trying to defend and protect herself.

Neighbours had been calling police about O'Neill for 30 minutes before the fatal attack. O'Neill had a history of mental illness and had spent periods receiving voluntary inpatient psychiatric care for a decade - most recently just weeks earlier.

O'Neill, 30, was found not guilty of Ms Steenbeek's murder on Monday, on grounds of mental impairment. Prosecution and defence experts agreed in the Supreme Court he was in an acute psychosis when he attacked Ms Steenbeek.

He'll be held in prison until a bed at a mental health facility becomes available. His period of supervision will be determined at a later court hearing.

Neighbours and O'Neill's housemates had noticed his behaviour in the lead-up to the incident.

He was described as a socially anxious person who could go through extreme mood changes. He became manic and obsessive at times, and was that day.

Housemates said he was manic and rambling as he left to see his girlfriend. A few minutes later they saw him trying to climb into a storm water drain.

A neighbour came across O'Neill crouching in the street while others were drawn into the street by his strange behaviour.

There were multiple calls to emergency services, asking for police and paramedics, but local officers weren't dispatched until a flurry of calls about Ms Steenbeek's screams.

O'Neill is due back in court on August 4.

Australian Associated Press