The five victims of the horrific mass killing discovered in Bedford on Sunday have been confirmed as three generations of the same family.

Forensic officers remained at the crime scene overnight after a man aged in his 20s went to a police station in WA’s north-west and sent them to the Coode Street property.

The victims include mother Mara Quinn, her three and a half-year-old daughter Charlotte, and twins Alice and Beatrix and the childrens’ grandmother.

The man, who was custody being questioned on Sunday night, is known to the victims but police have not revealed what he told officers.

The gruesome discovery marks the third case of a mass killing in WA this year.

Camera Icon Forensic officers at the scene of a mass killing on Coode Street. Credit: Bohdan Warchomij

Assistant Commissioner Paul Steel said at a press conference on Sunday it was still unclear how long the bodies had been at the house before they were discovered.

“This is a tragic event that will have no doubt have an impact, not only on the family and friends of the deceased, but for the whole of the community, those first responders who were faced with attending a scene with multiple deceased people,” he said.

“It does send a ripple through the community of Western Australia.

“Part of the homicide squad investigation is going to try and identify the time line of all events which led to this matter. How long the bodies have been there will also form part of that timeline inquiry.”