Hours later, the truck driver hit and killed four police officers on Melbourne's Eastern Freeway.

Singh's daughter, Harpreet Bajwa, said she told him to stay home on April 22, 2020.

It was not uncommon for him to speak about seeing witches, ghosts and aliens that changed faces or clothes. But that day was different.

"The way he was acting that day scared me and I told him he was going to kill someone if he drove," the 21-year-old told Melbourne Magistrates Court on Monday.

"His voice was racing, his pupils were bigger. He seemed pretty terrified."

She gave evidence on the first day of a committal hearing for trucking boss Simiona Tuteru.

He faces 82 charges, including the manslaughters of Senior Constable Lynette Taylor, Senior Constable Kevin King, and constables Glen Humphris and Josh Prestney.

The committal is set to examine what the Connect Logistics manager knew about Singh's impaired state and what he did, if anything, to encourage him to drive.

Singh himself is also expected to give evidence against his boss next month.

Among dozens of charges, Tuteru is charged with multiple breaches of heavy vehicle regulations, including directing or requiring Singh to work while fatigued.

Other charges include obtaining financial advantage by deception, for time sheets submitted in a false name to hide the real number of hours worked.

Singh was last month jailed for up to 22 years for culpable driving causing the officers' deaths.

He had barely slept and was high on drugs when he crashed a semi-trailer into the emergency lane where the police were dealing with speeding Porsche driver Richard Pusey.

Earlier that day, he told his family work had sent him home, told him to see a psychiatrist and that he had to go back for a meeting otherwise he'd lose his job.

His daughter recorded him on her phone "saying a lot of things that didn't really make sense".

She told the court she never saw her dad take drugs but had noticed his mental health decline.

He suffered from undiagnosed bipolar disorder and depression, according to his son Gurdeep Bajwa.

"I don't believe my dad would try and hurt someone," the 23-year-old said in documents released by the court.

After the crash, Singh called his wife from what sounded like an ambulance and said he may have killed two police officers.

"I started shaking and couldn't breathe. I put the phone down on the bench and my son and daughter were just holding me," Amarjit Bajwa said.

The committal, which will determine if there's enough evidence for Tuteru to stand trial, is expected to continue on Tuesday.

Singh's supervisor Stephen Harrison is expected to give evidence.

Australian Associated Press