Edward Livingstone was ''competent to make his own decisions'' and was ultimately responsible for the death of Bradley (9) and Ellen (6), Chief Coroner Judge Deborah Marshall said in her findings from the inquest into the trio's deaths.
However, multiple failings by police, social agencies and mental health professionals meant the murderous intent of a vengeful father was missed.
''We do not know what the trigger was on 15 January,'' Judge Marshall said in the findings released yesterday.
''Edward was competent to make his own decisions and appeared until the very end to be 'hedging his bets'.
''On the one hand, he was taking actions about future events - his new relationship, his new flat, checking the Barnardos appointment, getting his prescription filled. At the same time, he had taken the spare key from [one-time flatmate Philip] Mans' house and made sure he had access to 9 Kiwi St [the family home] through the rarely used door.''
In the months before the deaths, Livingstone was twice charged with breaching a protection order preventing him from contacting Ms Webb.
Livingstone had been drinking in the hours before he killed his children, but toxicology reports showed his blood-alcohol level was 47mg of alcohol per 100ml of blood, well below the then legal limit to drive.
Livingstone burst into Ms Webb's St Leonards house about 9.30pm on the day of the shootings, carrying a stolen 12-gauge Stoeger shotgun, cartridges and a plastic container of petrol.
Ms Webb fled her bedroom and left the house, running to the home of her neighbours, Christopher and Melanie Foot.
She heard several shots while escaping.
Livingstone shot the children as they slept in their beds, firing three cartridges into Bradley's chest and one at Ellen.
No marks were found on Bradley's body to indicate a struggle had taken place and Ellen was shot while lying underneath her duvet, Judge Marshall said.
Livingstone then turned the shotgun on himself in the front bedroom of the house he formerly shared with Ms Webb and their children.
Judge Marshall noted that although red flags were missed by the agencies protecting Ms Webb and her children and that failings allowed Livingstone's risk to his family to go undetected, that ''best practice'' by police and various social agencies might not have ''altered the tragic outcome''.
Judge Marshall recommended that health professionals needed to take care when providing reports to court.
Police should also review how incidents of family violence were recorded and whether the adult sexual assault regime instituted in the Southern district should be implemented nationally.
Police missed key warning signs, such as the reported rape of Ms Webb by Livingstone and spent bullet casings which Livingstone gave to the children, ostensibly as a present.
Mental health professionals tasked with caring for Livingstone had provided letters which were used by his legal team during the court proceedings which followed his protection order breaches.
The Family Violence Inter-agency Response System (FVIARS) partners, charged with protecting the victims of family violence, should regularly audit which cases were discussed, what information was provided at meetings between the agencies and what actions were taken following meetings, Judge Marshall recommended.
