The man who shot dead a mother and daughter in a Perth suburb last week had a stash of 13 guns in his house, it has been revealed.

In an attack labelled “chilling and horrific” by Western Australian Premier Roger Cook, 59-year-old Jennifer Petelczyc and her 18-year-old daughter Gretl were killed by the gunman as he searched for his ex-wife.

She was believed to have been staying in the Petelczycs’ Floreat home after leaving her relationship.

Her former partner, who has been named as 63-year-old Mark Bombara, turned his gun on himself after shooting the Petelczycs.

The killings have raised pressure on the WA government, which is in the middle of toughening state gun laws.

A $64 million buyback scheme is under way and legislative changes are on foot to restrict the number of firearms people can own.

Last week’s shootings have prompted the government to consider even stricter gun laws and to concede more needs to be done to combat family violence in the state.

Police Minister Paul Papalia said Bombara legally had 11 firearms on a recreational shooters’ licence. He had two handguns on a collectors’ licence and also had an ammunition collectors’ licence.

They were found in his waterfront mansion in Mosman Park when police searched it on Saturday. Under the revised WA laws, Bombara would have been allowed five weapons.

“There is no reason a person living in Mosman Park should be able to legally own 13 guns. It’s hard to fathom one man, 13 guns legally owned, right in the suburbs of Perth,” Cook said on Monday.

WA police said Bombara was known to them, but had no history of violence. Papalia said the gunman’s ex-wife went to police at the end of March seeking help to get her belongings from the couple’s former home.

Police are not treating last Friday’s twin shooting as family violence because there was no family connection between Bombara and the two women.

Cook, who earlier described the shootings as “senseless” and said the Petelczycs were innocent people who had died helping a friend in need, appeared to disagree on Monday.

“As a community, we all need to do more to tackle the root causes of family and domestic violence. This was a crime motivated by family and domestic violence,” he said.

Earlier, Cook said Bombara’s wife had been supported as part of the relationship breakdown.

“We want to continue to understand what extra steps they could have taken if we had different firearm laws in place,” he told ABC Radio Perth.

“Obviously, as a government, one of my key objectives, is to understand what more can we do to equip the police to be able to support people in these situations.”

On Monday, WA Environment Minister Reece Whitby insisted the incident was domestic violence, although he stopped short of urging police to reconsider their position.

“Everyone knows what happened here,” he said, according to a report in WA Today.

“A man believed that he had a right to harm and threaten women, and it was related to domestic violence – it’s an outrage.”

State Liberal leader Libby Mettam expressed a similar view, saying it was hard to understand how the incident was not considered domestic violence.

Women’s safety charity White Ribbon Australia said it was “enraging that once again a man has resorted to murder as the ultimate full stop on the end of a relationship”.

“In this instance, the women were murdered because they provided support to the killer’s wife when the relationship ended,” chief executive Melissa Perry said.

“Murdered for supporting a friend.”

Police were called to the Petelczycs’ home in Perth’s affluent western suburbs about 4.30pm on Friday after reports of gunshots. They arrived as the last shot was fired.

Jennifer Petelczyc died at the scene.

Gretl was rushed to Royal Perth Hospital but she could not be saved. She died on Saturday.

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-with AAP