The Victorian Supreme Court has heard it was a "conscious, voluntary and deliberate act" when a Hawthorn man threw his daughter off Melbourne's Westgate Bridge.

Four-year-old Darcey Freeman died after her father, Arthur Freeman, 36, threw her off the bridge in peak hour in January 2009.

She reportedly fell like a "rag doll" for 58 metres until hitting the water.

Freeman has pleaded not guilty to her murder.

Prosecutor Gavin Silbert SC told the court it was to be Darcey's first day of school.

He told the jury her two brothers were also in the car when Freeman pulled into the inbound emergency lane of the bridge and asked Darcey to walk to the edge.

He has told the court it was a deliberate act from a man who was extremely bitter about his marriage break-up.

Freeman was also angry because a day earlier the amount of time that he had custody of his children for had been reduced, the court was told.

He and his three children had spent the night at his parents' house on Victoria's Surf Coast.

Minutes before Darcey was thrown from the bridge, Freeman told his former wife Peta Barnes over the telephone to "say goodbye to your children", adding "you will never see them again".

Freeman also spoke to a friend in the United Kingdom and said everywhere he turned "there were angry women against him".

But defence barrister David Brustman SC says his client cannot be held responsible for murder.

He told the court that although "on any view, the facts of the case constitute a horror", Freeman was of a "highly disordered" mind and mentally ill at the time.

The trial continues.

- ABC/AAP