Two-year-old twin girls, their three-year-old sister, mother and grandmother have been found slain in a Perth home, the victims of the third mass killing in Western Australia this year.
The bodies of Mara Quinn, aged in her 40s, her three-year-old daughter Charlotte, twins Alice and Beatrix, and their grandmother were found at a Bedford home, in Perth's east, on Sunday.
It comes after the shooting deaths of three adults and four children in Osmington in regional WA in May, and the deaths of a mother and her 15-year-old daughter and eight-year-old son at Ellenbrook, in Perth's northeast, in July.
A man in his 20s turned himself in at Karratha police station, some 1500 kilometres from Perth, on Sunday, prompting police to visit the Coode Street home where they discovered the bodies about midday.
It is believed the man also lived at the home, although police have not confirmed this.
"The man currently assisting police remains in custody. No charges have been laid at this time," police said in a statement on Monday.
Homicide detectives and specialist forensic police are continuing to comb the home for evidence.
"Depending on the size of that crime scene, that will take a period of time and it could be a number of days," Assistant Commissioner Metropolitan Region Paul Steel said.
A bouquet of red roses with a card saying "rest in peace, neighbours" has been placed on a light pole near the house.
According to her Facebook page, Mara Quinn became engaged in August 2014 and the couple had their first child in March 2015.
It is understood there was a significant age difference between the pair.
A young father, who is building a house nearby, told AAP: "I've got a two-year-old girl - I can't rationalise anything that would cause someone to do that."
An elderly woman who also lives nearby said: "I don't know what's coming to this world."
A couple who live a few doors down from the house said they did not know the family but were horrified when police knocked on their door on Sunday and told them what had happened.
An elderly man who has lived in the neighbourhood for decades said it was usually tranquil.
"It's normally a quiet place," he told AAP.
Deputy Premier and Heath Minister Roger Cook said it was not yet known whether there was a common cause between the three tragedies, but added that mental health was his most challenging portfolio and the situation seemed to be getting worse.
"We have limited resources, we are constantly looking at new ways that we can apply those resources to provide the appropriate level of support," Mr Cook said
He described the deaths as horrible.
"Our heart goes out to the family and friends of all involved, but also to the first responders who obviously had to witness that horrible situation," he told reporters.
"I want everyone just to hug their kids, hug their family today. This is a horrible event and it's very upsetting."
If you are concerned about your own wellbeing, are experiencing a personal crisis, or are concerned about someone else, contact Lifeline on 13 11 14 or at www.lifeline.org.au.