The State’s top cop has revealed how the investigation into the family’s cause of death is progressing.

The investigation into the Mosman Park double-murder suicide has been handed over to the WA coroner, but the State’s top cop says it could be months before reports reveal how two young brothers were killed.

Brothers Leon, 16, and Otis, 14, and their parents Jarrod Clune and Maiweena Goasdoue were found dead inside their Mott Close home on January 30.

A person known to the family, believed to be a carer for the boys — who had autism — found a note on the front door which warned them to not go inside and call police.

Both boys are believed to have been killed by their mother and father, before the parents took their own lives.

Police Commissioner Col Blanch on Wednesday confirmed the active investigation by his officers had come to an end and it was now “under control of the coroner”.

When questioned further over whether police had received the toxicology results, which could shed light on how the children died, Mr Blanch said: “I don’t know the answer to that, I would suggest not given the timeframe these things can take.”

It comes just weeks after Cottesloe MP Sandra Brewer demanded a coronial inquest be held to determine whether the tragedy could have been prevented.

“There is a deep sense of grief and concern across the community, and a strong desire to understand how and why this tragedy occurred,” Ms Brewer said.

“This is a matter of profound public interest, and as a community we should know what happened prior to this incident.

“I support a coronial inquest so the community can understand what happened and consider recommendations to prevent future tragedies, and I therefore call on the Premier and Attorney General to direct the coroner to hold an inquest.”

Disability Discrimination Commissioner Rosemary Kayess echoed calls for for an inquest, saying the incident highlighted the immense stress of those who didn’t receive adequate support.

Recent reports have suggested one of the brothers had their NDIS funding cut.

“A coronial inquest is urgently needed to ensure strong investigative powers to respond to this tragedy and to identify the underlying and systemic issues that led to the parents’ actions, and to provide a sense of justice for Otis and Leon,” she said earlier this month.

“I call for urgent action on the 222 recommendations of the Disability Royal Commission, which found that people with disability in Australia have been systematically devalued.

“Without meaningful action, tragedies like this will continue.”

Premier Roger Cook has resisted calls for an inquest, saying it is up to the coroner to make a decision.

But under the WA Coroners Act, the State Government and Attorney General have the power to force the coroner to hold an inquest.

“I understand there’s speculation around NDIS support, school support and things of that nature,” he said earlier this month.

“The coroner, ultimately, is the one who’s responsible for making a decision about any form of inquest.”

The coroners court has been contacted for comment.