Outsiders viewed the executions as unimaginable but John Edwards had meticulously prepared his children's murders.
Police now question whether the Sydney pensioner had outside help.
Jennifer, 13, and Jack, 15, had never told their estranged father of their new home before he followed his daughter on her way home from school and shot them both dead in West Pennant Hills in July 2018.
Edwards, who had waged psychological and physical assaults on a string of partners for decades, then drove to his Normanhurst home and shot himself.
The trio's inquest, due to resume Tuesday, has been told the 67-year-old had been planning for at least six months to kill his children.
Based on his history and a note found in Edwards' pocket, the lead police investigator suspects the financial planner could have hired private investigators to find the family.
"(The note) appeared to be a timetable of Jennifer's movements to and from school," Detective Sergeant Tara Phillips told the NSW Coroners Court on Monday.
Edwards had previously used a private investigator to track his most recent ex-wife and the children's mother, solicitor Olga Edwards, the officer said.
Having tracked down and spoken to numerous ex-partners of Edwards and many of his children, the detective painted a picture of a controlling, narcissistic, self-centred and calculating man.
"He had a history of exerting control over the women in his life and his children. He had a propensity for domestic violence," she said.
When Edwards' 15-year marriage to Olga broke down in 2016, he "became consumed with maintaining a relationship with Jack and Jennifer" and blamed Olga for the children's estrangement, the detective said.
After the children's murder, Olga detailed to Det Sgt Phillips how Edwards had over the years physically abused the children over minor things, such as touching his phone or CD collection.
But exactly how he found the family in West Pennant Hills may never be known.
"He'd set fire to all his electronics, so we were unable to extract (anything)," Det Sgt Phillips said.
Olga Edwards' boss David Brown is expected to tell the inquest on Tuesday about how he was involved in a significant argument with Edwards when helping Olga collect her belonging from the marital home.
Mr Brown represented Olga during her Family Court proceedings against Edwards.
The inquest, which is expected to run until September 25, will closely examine how Edwards was able to legally acquire the handguns he used to kill his children and then himself.
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Australian Associated Press