The officer who shot dead a Melbourne father moments after he killed his own son has put the troubled man "at peace", the slain boy's mother says.
Four uniformed officers were confronted by the knife-wielding 54-year-old at the Tyabb cricket oval on Wednesday evening.
Gregory Anderson had just killed his son, 11-year-old Luke Batty, and was refusing to drop his knife, police say.
But the officers didn't have Tasers and had to draw their firearms when he kept rushing towards them.
Capsicum foam had no effect.
He was shot once in the chest and died in hospital.
The boy's mother, Rosie Batty, says Mr Anderson had a history of violence and mental illness.
She said the officer who killed Mr Anderson faced an aggressive man who was resisting arrest and he shouldn't feel bad for what happened.
"He's put a man at peace," she told Triple M on Friday.
"Greg was tormented and there was no future in his life for him. But he shouldn't have taken my little boy with him."
Victoria's rollout of Tasers has only reached a handful of regional centres and specialist groups during a multi-year rollout, expected to end by mid-2015.
Police want to give officers the electro-shock devices as an alternative to lethal force during violent confrontations.
But Chief Commissioner Ken Lay says it wouldn't have mattered if Tasers were available in this case.
He said the decision to draw a firearm was the right one.
"One of my members was faced with someone who just murdered an 11-year-old child and is running at them with a knife," he said.
"I think the option is pretty clear."
The homicide squad, the force's internal investigations unit, and the state's anti-corruption watchdog are all reviewing the fatal police shooting.
A coronial inquest will also be held.