A Supreme Court jury has found Robert Farquharson guilty of deliberately killing his sons, Jai, Tyler and Bailey when he plunged his car into a dam on Father's Day in 2005.

After an 11-week retrial, the jury found Farquharson, 41, guilty of three counts of murder.

In finding him guilty, the jury rejected his claim he had blacked out from a coughing fit when the car plunged into the water.

As the charges and their verdicts were read out one by one, Farquharson sat with his face crumpled, shaking his head in bewilderment.

His sister sobbed while members of the jury were also reduced to tears.

As his estranged wife Cindy Gambino - the mother of the children - and her mother Bev left the court, the emotional strain of an 11-week trial took its toll.

Bev's knees buckled, she fell to the floor and had to be assisted into a taxi.

In 2007, Farquharson was convicted and sentenced to serve three life sentences for murder.

He successfully appealed against the conviction and the Court of Appeal ordered a retrial in 2009.

There the reasons why his children drowned were again put to the test.

Farquharson walked away uninjured when he crashed his car into a dam near Winchelsea.

The bodies of Jai, 10, Tyler, 7, and Bailey, 2, were found trapped inside the car, their seatbelts unbuckled.

Just hours earlier, they had given their dad a framed photo of themselves as a present and were looking forward to spending the day with him.

The triple murderer always maintained he blacked out from a coughing fit when the car veered off the Princes Highway and plunged into the water.

Taking the stand to give his version of the fateful night, Farquharson was forced to explain why he did not try to get his kids out before the car nose-dived.

He said he initially thought he had crashed into a ditch.

The court was told he had dived down three or four times to try and reach them, before he flagged down passing motorists, gibbering incoherently and demanding to be taken Ms Gambino.

"It's just something I had to do, I can't explain it," he said.

"She's the mother of my children and I wanted to tell her I had an accident."

A teary Farquharson recalled his sons' funerals and refuted claims by his former friend, Greg King, that he had planned to "pay his wife back big time" by taking away her children.

He admitted that maybe "payback" had been the wrong choice of words and he had simply meant he planned to get on with his life.

Tearful testimony

Farquharson's testimony was one of many differences to separate the retrial from that held in 2007, along with that given by Cindy Gambino, who dramatically turned against the man she had once supported.

In harrowing testimony, punctuated by heavy sobbing that forced the trial to break frequently, Ms Gambino said though she had once stated he had been a loving father, Farquharson had a "love-hate relationship" with the boys.

For several days she was taken through her final moments with her sons and the night she stood by and watched as people tried in vain to find her sons in the dark water.

She said Farquharson had stood there, arms crossed, looking like "he had just lost his push bike".

When asked why she spurned her ex-husband's offers of comfort on the night, she snarled "Why wouldn't I? He killed my kids."

In support of Farquharson's claim he was unconscious at the wheel, his defence counsel Peter Morrissey called on several witnesses, including sufferers and doctors who spoke of the debilitating effects of a rare condition known as cough syncope.

An inmate testified how he had seen Farqharson black out from a coughing fit in his cell, breaking his leg in the fall.

His sister and aged care nurse, Carmen Ross, was also recalled to explain how in the final weeks of the trial Farquharson had dropped "like a sack of spuds" from his latest attack bought on by the affliction.

The explanation was inconsistent with crash reconstruction tests carried out by Victoria Police.

Prosecutor Andrew Tinney SC argued the tests revealed the car was steered three times along its path from the road to the dam.

Senior Constable Glen Urquhart from Victoria Police's major collision investigation unit believed one distinct turn of the wheel enabled the car to dodge a tree.

Witnesses' account

Farqharson's explanation was also at odds with new evidence presented by eye witness Dawn Waite, who until recently had never come forward to police.

She was the last person to see Farquharson's car travelling along the highway before it left the road.

Ms Waite said the car was travelling at half the speed limit, its brake lights flashing intermittently in the dark.

As she overtook it, she noticed three children in the back seat.

She recalled she had not seen the driver coughing as she overtook him.

Just minutes later, Ms Waite said she watched in her rear-view mirror as the car veered to the right, as if the driver had found a turn-off he was looking for.

It was only after she saw vision of a car being pulled from the dam on the TV news she became concerned about what she had seen.

In his closing address, Mr Tinney asked the jury to consider the likelihood of events leading to the death of the boys.

"It's a little bit unlucky that this shockingly unlucky event happened to a man who had threatened to pay his wife back big time, isn't it, members of the jury, and now they're dead, the children," he said.

"What a dreadfully, shockingly, unbelievably unlucky man the accused was on that day if he was not a heartless murderer."

Mr Tinney said this defied belief.

He summed up Farquharson as being a man determined to get back at his wife, who had left him and started a new relationship.

"He hated her, he hated the fact she had moved on with another man, he hated his life... He hated the fact he had to pay maintenance for the children," he said.

"The accused deliberately drove his vehicle into the dam to murder his children and was not an innocent victim of an unlucky coughing fit leading to unconsciousness."

Farquharson will be sentenced at a later date.