Supreme Court Justice Lex Lasry described Charles Mihayo's crimes as "hideous" and said that he was at a loss to understand why the children had had to pay with their lives so Mihayo could cause suffering to his former wife.

Justice Lasry said the 36-year-old's actions were devoid of any justification or explanation.

"It is difficult to think of more serious murders," the judge said on Thursday when jailing Mihayo for life with a non-parole period of 31 years.

Mihayo had pleaded guilty to murdering four-year-old Savannah and three-year-old Indianna on Easter Sunday.

He had played hide and seek with the girls before smothering them with a pillow.

Justice Lasry said he rejected Mihayo's claim that the murders of his young, vulnerable, trustng daughters had been spontaneous.

The judge said he believed Mihayo had decided to kill his daughters after they had arrived at his Watsonia apartment because he been angry over the failure of his marriage.

Justice Lasry said the murders had been strongly motivated by Mihayo's hostility towards his ex-wife.

"What is absolutely clear to me is that your act of killing them was inextricably connected with what you saw as your ex-wife's unfair treatment of you and the hostility you felt as a result," the judge said.

"You determined that she would pay a price and inevitably so would your children - with their lives.

"No matter how you felt about what had gone on before, what you did was a despicable act of killing and nothing that you described could even logically explain it.

"You gave in to the basest of instincts - revenge."

He said Mihayo did not seem to be remorseful for his actions. Mihayo had acknowledged what he did was wrong but the judge was not sure he regretted what he had done.

Justice Lasry said he had carefully watched Mihayo's police record of interview where he did not utter one word of sorrow or regret but admitted the murders might have been carried out because of vindictiveness and selfishness.

Mihayo, a Tanzanian national who is a permanent resident of Australia, told his ex-wife, the girl's mother, on April 19 that he wanted to "say goodbye" to the girls and "see them one last time", so a meeting was planned for the following day.

The girls' mother took them to see Mihayo, who lived in a self-contained unit at the back of her mother's house at Watsonia, just after 2pm.

He dressed the girls in white dresses and filmed them dancing to a song from the movie Frozen before suffocating them.

Mihayo then called police before taking the children into the bathroom where he bathed and re-dressed them.

When police arrived Mihayo opened the door with a towel in his hands and said, "It's done. I've killed them. I've killed my kids."

Mihayo told police he understood what he did was wrong and took full responsibility for his actions.

He claimed there was no good reason for what he did but it made sense to him at the time.

He said he did not plan to kill his children, but would not say why he did it, saying investigators would not understand what he had been through and providing a reason would not make any difference.

The Crown case was that Mihayo killed his daughters as an act of revenge against the girls' mother.

Mihayo had been fighting for access to the children since a separation in 2009 and both he and his former partner had hired lawyers in the weeks leading up to the murders.

Four days before killing the girls, Mihayo had Googled the question, "How can I kill my ex-wife".

Defence barrister Tim Marsh had told the court Mihayo never knew his father and had indicated "there was some particular horror in his mind that his children would grow up without knowing their father".

Justice Lasry said Mihayo's breach of parental trust was "almost beyond belief".

"Our community continues to be shocked by the actions of fathers like you killing their children in an atmosphere of marital discord. I am unable to understand why it is that those who are undeniably innocent or any wrongdoing pay with their lives so often."

The girls' family released a brief statement following Mihayo's jailing saying there was no adequate punishment or jail sentence for their murders.

The family said the girls would be "forever missed, loved and never forgotten".