Father in murder-suicide planted bombs in family car

A father who killed his pregnant wife and eldest son rigged the family car with petrol bombs before ploughing it into a tree.

An inquest has heard the double murder-suicide had been planned for months with the Sydney man performing practice runs, maintaining a diary and considering whether he could disable the car’s airbags.

Engineer Darren John Milne, 42, murdered wife Susana Estevez Castillo, 39, and their 11-year-old son Liam on February 1, 2015 when their car veered off the road at Fountaindale on NSW Central Coast and hit a tree.

The couple’s youngest son, Benjamin, who was seven at the time was placed in an induced coma and survived.

The Central Coast Gosford Express Advocate revealed the extent of Milne’s plans after an inquest at Wyong Local Court heard the 42-year-old had filmed “10 practice runs” on his dash cam two days before the crash and had identified “heavily wooded” roads between Sydney and the Central Coast.

Leading Senior Constable Peter Mason discovered the elaborate wiring of petrol bombs when he took the engine bay apart.

The wiring connected 12volt batteries to two 500ml flasks filled with petrol that failed to detonate at the time of the crash.

Detective Senior Constable Karen Kennedy, told the inquest an iPad had been recovered from the car that possessed files that could be considered “a suicide note”.

“From this point on I need to be totally focused, forget everything else,” it read.

“Take DVR (dash camera) out of the car so as to not raise suspicion. Copy work personal stuff to portable disk. Start taking personal stuff home.”

It was reported the file titled: 'Plan - Stage 2' and dated September 20 - almost three months before the crash - revealed the elaborate extent to which Milne had planned the crash.

Senior Constable Kennedy also revealed that Milne had been seeing a psychiatrist since 2007 who diagnosed him with "some kind of depression or ADD".

Estevez Castillo was a full-time carer for their two sons who had special needs due to being diagnosed with "fragile X" syndrome.

The Central Coast Gosford Express Advocate reported that Police believed Milne performed the murder-suicide out of the fear his children would not be able to cope with their disabilities.