The 54-year-old man who murdered his own son at a Melbourne cricket ground should have been arrested weeks before the killing, Victoria's police chief says.
Police have confirmed Gregory Anderson was wanted on five outstanding warrants when he killed 11-year-old son Luke Batty at the Tyabb oval on the Mornington Peninsula.
But the police force's outdated computer system was one reason police were unaware there were outstanding arrest warrants when he was questioned in January about several assaults.
Chief Commissioner Ken Lay says the computer database has a two-week lag time on showing such information.
"If police would've gone to that address a day later, those warrants would have been visible," Mr Lay told reporters on Friday.
But Mr Lay stressed the IT failure was only one piece of a complicated case.
"This is not me blaming an IT system for the death of a young boy," he said.
"It is one part of a very complex issue for us."
There was also no way of knowing if Mr Anderson would have been held in custody or immediately bailed - even if he had been arrested prior to the murder, he added.
The boy's mother, Rosie Batty, was also aware of the outstanding warrants when Mr Anderson showed up at cricket practice on Wednesday evening.
Ms Batty said she didn't have a problem with letting Mr Anderson play with their son that night as she wanted Luke to know his father.
Luke was then killed as practice was winding down.
Witnesses told police the man struck his son in the head with a cricket bat. It's believed he then turned the knife on the boy.
"The worst thing that could have ever happened to me has just happened," Ms Batty told Triple M radio station.
"And a little boy, who was innocent, because of a selfish act from his father who wanted to die, wanted to take him with him."
Mr Anderson was shot dead by police after the killing.
Mr Lay said he was confident his officers acted appropriately, considering the threat they faced against their own lives.
He will be meeting with the government about the IT system failure shortly.
Several reports have highlighted how the force's antiquated IT system has been neglected for 15 years.
Police Minister Kim Wells said $20 million had been put into fixing the system in the latest state budget.
"It's an incredibly sad situation, but we need to make sure we have all the facts, evidence and information for us before we can step this forward," he told reporters.
