An ACT Supreme Court jury deliberated for about three-and-a-half hours before finding Anthony Paton, 56, guilty of culpable driving causing death and culpable driving causing grievous bodily harm.

Andrew John Paton, 29, of Ngunnawal, died after the Commodore his father was driving along Gundaroo Drive about 1pm in July 2009 hit an oncoming Toyota Yaris.

The front passenger of the Yaris also received serious injuries in the collision.

During the trial, jurors heard the offender had an expired driver's licence, returned an alcohol reading of .281, and the car was unregistered at the time.

Paton, the deceased and two other men had been drinking on the morning of the smash.

One of the men, a rear passenger in the vehicle at the time of the crash, told the court from the witness box Paton had been driving erratically - speeding and trying to slide the car around corners - when he lost control of the vehicle and collided with the oncoming car.

But Paton's lawyers argued the fatal accident had been caused by a passenger activating the car's handbrake moments before the collision.

The witness's voice could be heard mentioning a handbrake in the background of a triple-0 call, made by a passer-by who stopped to help, but he told the court it was not engaged and he did not know why he had said it.

Jurors also heard conflicting evidence from two experts about proof of handbrake activity before the crash.

In final submissions, Crown prosecutor Shane Drumgold said causation was the critical issue in the trial.

Mr Drumgold told jurors to ask themselves a series of questions, including whether Paton's driving contributed significantly to the collision and therefore the death and injuries.

But defence barrister James Jeffrey pointed to inconsistencies between what the passenger told the court about the handbrake and what could be heard in the background of the emergency phone call.

Justice Hilary Penfold on Thursday thanked jurors for their assistance before sending them home.

The judge revoked Paton's bail.

He will reappear for sentence in August.