A Sydney father who murdered his children in a "planned and premeditated" attack before taking his own life had an arsenal of guns in his house, including two powerful weapons used in the shootings.
And while neighbours knew the family had some challenges, locals have been left shocked and horrified by the crime.
John Edwards was found dead the morning after he killed his 15-year-old son and 13-year-old daughter in a bedroom at their Hull Road home at West Pennant Hills about 5.20pm on Thursday.
The 68-year-old's body was discovered by police four kilometres away in his Normanhurst home about 12 hours later.
They believe he took his own life very soon after the shooting, which was overheard by neighbours.
Acting Assistant Commissioner Brett McFadden said it was too early to say exactly what happened in the West Pennant Hills home.
"The information we've gleaned ... leads me to believe this was premeditated and planned," Mr McFadden told reporters in Sydney on Friday.
Police were aware of Mr Edwards over matters in the past but he had no contemporary issues with the law.
He had been involved in a custody battle with the children's 36-year-old mother Olga Edwards for two years following the breakdown of their marriage.
But the nature of their relationship and any violent incidents between the pair is still being investigated.
Juliette Hackett, who lives a few doors down from Mr Edwards' home, she didn't know the family well but the teenagers "had their challenges".
"I feel very sad that John felt that there was no alternative than the horrific thing he did," Ms Hackett told AAP on Friday.
Mr Edwards, described as a "recluse" by another neighbour, was a financial planner and volunteered with the NSW Rural Fire Service, Lions Club and Pennant Hills Junior AFL Club, according to his LinkedIn page.
Two "quite powerful" handguns, registered in the father's name sometime this year and used to kill the children, were found at the Normanhurst home, Mr McFadden added.
A number of other guns owned by Mr Edwards were also found.
Mr McFadden said the mother, who arrived at the house shortly after the shooting, was treated by paramedics for severe shock.
Ms Edwards, a solicitor at Brown and Partners Solicitors in Woolwich, was taken into the care of friends and police after the attack.
One neighbour said Mr Edwards, who was often seen walking his border collie in the area, never waved to anyone.
"That stood out because everyone here walking their dogs waves to each other," they told AAP.
"It's a terrible tragedy that he thought that was the only option, to take the kids instead of letting them live with their mother."
Another neighbour said Mr Edwards had little to do with anyone.
"He wasn't a gardener which you can tell from how overgrown his place was," he told AAP.
NSW Ambulance Inspector Kevin Sweeney described it as an "extremely distressing and stressful situation" for paramedics who arrived at the scene.
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