A South Australian man will spend at least 23 years in jail for murdering two people in a failed attempt to kill himself in a road crash. Michael Frank Knowles was found guilty on Monday of two counts of murder over deliberately driving his car into the path of an oncoming vehicle in 2014.

Four friends were travelling in the oncoming four-wheel-drive, with James Moore and Natasha Turnbull killed and Amy Jones and Jason Bristow injured.

They were returning to Whyalla from Coffin Bay after spending a day at the beach.

After taking sentencing submissions in the Port Augusta Supreme Court, Justice Trish Kelly on Tuesday imposed a mandatory life sentence on Knowles with a non-parole period of 23 years.

She also jailed him for at least six years on two counts of causing death by dangerous driving but ordered the term be served concurrently with his sentence for two counts of murder.

At the opening of his trial last week the court was told Knowles had set out to kill himself when he drove his Nissan Patrol into the path of Mr Moore’s Mitsubishi Pajero.

Prosecutor Mark Norman said Knowles must have known that driving his car into the other vehicle with sufficient force to kill himself would probably kill or cause serious harm to anyone in the other car.

‘But despite that knowledge, and instead of choosing to drive into a tree or a rock or a brick wall or even an empty parked car, he chose to drive straight into James Moore’s Pajero,’ the prosecutor said.

Knowles admitted causing the crash and being drunk, but disputed prosecution allegations that he was trying to take his own life.