A Melbourne man who murdered his two young daughters by smothering them with pillows has refused to disclose a motive for his crimes.

Charles Mihayo smothered his daughters Savannah, four, and Indianna, three, at his unit at Watsonia in April.

He pleaded guilty to the killings in August and faced a pre-sentence hearing today.

Prosecutors said the 36-year-old was locked in a bitter custodial dispute with his former wife at the time and acted out of revenge.

They compared his case to other Victorian child killers, including Donna Fitchett, Arthur Freeman and Robert Farquharson.

The Victorian Supreme Court heard Mihayo sent a text message to his former wife shortly before he killed them, suggesting she had "won" and he was giving up his rights to see the girls.

He told her he wanted to see them "one last time", and when she took them to see him he dressed the girls up in new dresses he had bought for them.

He then filmed them dancing to music, before smothering them with pillows.

But he later told his former wife: "Do you really believe I'd give up my flesh and blood just like that? You don't get to decide that for me."

The court heard the girls' mother was outside the unit at the time and her daughters had come outside to show her their new outfits, before they returned inside and the unit "went quiet".

When she asked Mihayo what had happened, he told her "you'll know when they get here", meaning the police.

At that point, the court heard the girls' mother ran next door to call triple-0.

Mihayo was arrested at the scene and confessed to police, telling them "there was no good reason" for the killings but they "made sense at the time".

The court heard he told police at the scene: "It's done. I killed them. I killed my kids."

When police asked why, he told them "you'd have to ask her", meaning his ex-wife.

Justice Lex Lasry told the court, there was "a very strong public interest in this case" and the community was entitled to "some sort of explanation".

But Mihayo's lawyer Tim Marsh told the court his client had specifically instructed him not to provide a justification for murdering his children.

He said his client was "a man, who on some levels is loving and caring, and capable of acting in such a way".

But Mr Marsh said "the answer...is something Mr Mihayo is not prepared to give".

Mihayo's issue 'with his ex-wife, not his children'

The court heard Mihayo had previously threatened to kill his former wife if she took the children away from him, and had told a co-worker he had been thinking of ways to kill her.

When his colleague expressed concern for his daughters he told them they would be in a "safe place".

Forensic psychiatrist Daniel Sullivan told the court Mihayo had not attracted the attention of child protection authorities, nor had anyone thought he might kill his daughters.

"This was not a man who had come to the attention of child protection," he said.

The court heard Mihayo was locked in a bitter custody dispute with his former wife. ( ABC News )

"His issue was not with his children but with his ex-wife?" Justice Lasry asked.

"That would appear to be the case, yes," said Dr Sullivan.

Dr Sullivan said research on fathers who killed their children was limited but Mihayo, who had migrated from Tanzania, was socially isolated and estranged from his family.

He also said Mihayo's relationship had crumbled and his mother had recently died, leaving him "emotionally overwrought".

"I think he certainly regrets the consequences of his actions," Dr Sullivan said.

"He'll certainly experience a very difficult time in prison."

Mihayo will be sentenced at a later date.