Officers found the suspect dead at a home in Normanhurst.
The scene of the shooting in Normanhurst, Sydney, and John Edwards.
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.
McFadden confirmed the teenagers' mother, aged 36, arrived at the house in West Pennant Hills shortly after the police and was treated for severe shock by paramedics.
"We will be extending that support through additional counselling services today", Mr McFadden said.
"We consider this to be very much a targeted incident and we do believe that it may well be domestic violence-related", said Brett McFadden, acting assistant commander of the NSW Police north-west region metropolitan command, adding that the scene was "harrowing".
Police say the parents' long-term relationship had broken down and a custody battle had been ongoing for about two years.
NSW Ambulance Inspector Kevin McSweeney said when paramedics arrived at the scene they were confronted with "an extremely distressing and stressful situation".
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It's unclear how many shots were fired but detectives are speaking with several witnesses to determine what happened.
Police said the man had been involved in a custody dispute.
"It's very early in the investigation in what can only be described as a tragic set of circumstance for the family", Assistant Commissioner McFadden said.
"Two teenagers were unfortunately deceased in their bedroom and unfortunately at that time there was nothing we could do to help them", he said.
Prime Minister Malcolm Turnbull described the killings as "a bad, awful tragedy".
The 68-year-old did not reside at the house. He was alerted to the incident when his daughter saw it on the news and contacted him before he came outside.
As forensic examinations of the home continued on Friday morning, it is understood the teens' bodies were removed just before 6am.
"I couldn't believe it", he said. "It's so horrific ... especially for such young people to be the ones killed".
08 Juillet 2018
08 Juillet 2018
08 Juillet 2018
08 Juillet 2018
08 Juillet 2018
08 Juillet 2018
08 Juillet 2018
08 Juillet 2018
