THE case of an engineer who filled his car with “petrol bombs” and drove into a tree, wiping out almost his entire family, has been called one of the worst examples of a murder-suicide.

The scathing comments about Darren Milne come in inquest findings into his death and those of his wife Susana Estevez Castillo, 39, and their son Liam Milne, 11.

The trio were killed along with Ms Castillo’s unborn baby on February 1, 2015 when Milne deliberately drove his Toyota Corolla into a tree at Fountaindale on the New South Wales central coast.

The youngest family member, seven-year-old Benjamin, was the sole survivor.

The 42-year-ol AusGrid engineer had planned the crash so carefully he filmed as many as 10 practice runs on his dash cam and visited the exact spot two days earlier.

He even wrote notes about disabling the airbags and a reminder to take the dash cam out of the car “as not to raise suspicion”.

A detailed note made months before the deaths revealed Milne had decided his family had to die “because there is too much conspiring against us” and “it is a good time to go — it is only going to get tougher as time goes on.”

All that put Milne in a different league, a coroner says.

It is unusual for a coroner to comment on the conduct of a person who has taken their own life. “Two other lives were taken by him and the actions of Darren Milne should attract more than the usual disapproval attached to murder and suicide,” Coroner David Day said in findings released on Tuesday afternoon.

He found Milne showed total “disregard” for his two boys lives, their human rights and the fact their fragile X syndrome (FXS) could be treated.

FXS is a genetic condition causing intellectual disability, behavioural and learning challenges.

He also didn’t take into account the fact he and wife may have died and the children survive, leaving them injured and without parents.

“He assumed successful execution of his plan without regard to the possibility that the front seat occupants, he and Susana may not survive, but that one or both the rear-seat passengers would survive, terribly injured, severely disabled or otherwise, or worse, be conscious, trapped inside the cabin when the car caught fire.”

The fuel canisters didn’t ignite, but the impact killed Milne and Ms Castillo instantly. Liam died at the scene while his younger brother Benjamin was seriously injured. He is now living with his mother’s family in the United Kingdom.

A witness, Colin Cooper, told the inquest he saw the Toyota leave the road like it was “exiting a freeway” and without breaking or swerving.

It then struck the tree — the car sustained massive damage to the front with the battery flying out of the engine bay and skidding along the road.

Two fuel canisters were found, each containing half a litre of fuel. Coroner Day said it was his view they had been purposely wired to ignite on impact.

An iPad was recovered that had a note made by Milne in September 2014 in which he detailed his despair about his children’s conditions — and in which he laid bare his belief nothing could improve the family’s fortunes.

“It’s not worth it, neither of us have the skills to make it work. We have both given it our best shot over a long period of time. There is too much conspiring against us. L and B are both happy, B doesn’t know it yet, it is a good time to go. It is only going to get tougher as time goes on. We have been completely S’d over.”

He went on to say how they could try and cope with the various conditions they had.

“They are going to have to manage ADD and diabetes, it is going to be too much. They need to exercise and manage their health, it is going to be hard to see this fail.

“Things are going to get progressively harder for Ben, he hasn’t seen any malice or bullying yet, but it is coming. From this point on, I need to be totally focused, forget everything else, need to source comfort from the fact.”

From then, he began to prepare by checking the airbags could be disabled and began sorting through the family affairs, including their medical records and leaving copies of important documents where they could be found.

He ended the note with: “Start cleaning stuff up.”

andrew.koubaridis@news.com.au