A South Australian teenager charged over a triple fatal crash will wait for a verdict after his trial in the Youth Court.
The 17-year-old boy has pleaded not guilty to three counts of causing death by dangerous driving.
Millicent residents Ned and Nan Walker and their daughter Sue Skeer died in a head-on collision on the Princes Highway at Suttontown in November 2020.
The boy's four-day trial in Mount Gambier finished on Friday, with closing submissions due to be heard next Thursday.
Prosecutor Aimee Winra said the accident was a "catastrophic tragedy".
She previously told the court the teenager, who had a learner's driver's licence, had "not been concentrating" with the car in cruise control when he drifted into the opposite lane and collided with the oncoming vehicle.
But the teenager's defence lawyer, Bill Boucaut, said any drifting into the incorrect lane was "momentary".
The trial's witnesses
Nine witnesses were called to the stand throughout the trial.
Senior Sergeant David Kuchenmeister from the Major Crash Section gave testimony about data that had been extracted from the car that was driven by the teenager.
He said the vehicle's speed "remained relatively constant" in the seconds before the crash, meaning it was "entirely plausible" the car was in cruise control.
The court heard the brake pedal was pressed in the 0.7 seconds before the collision.
Senior sergeant Kuchenmeister told the court tyre marks from the scene indicated the teenager had been driving on the wrong side of the road, and the cars were attempting to swerve away from each other.
The court also heard from paediatrician Dr Daham De Silva, who consulted with the boy from September 2017 to help the teenager manage his autism spectrum disorder, Tourette syndrome and attention-deficit hyperactivity disorder (ADHD) diagnoses.
Dr De Silva prescribed the medication Vyvanse to the boy in February 2020.
He said the medication "reduces distractibility" and "increases concentration" and had been successful in achieving that in the boy.
The court heard Dr De Silva was not aware the teenager stopped taking the medication in May 2020.
The boy's aunt, who was in the car during the accident, also gave testimony.
She told the court it was the oncoming car, driven by Nan Walker, that was on the wrong side of the road.
She said "it happened so fast" and she "didn't see them [the oncoming car] until they were there".
Sole witness for the defence, crash reconstructionist Chris Hall, told the court the evidence on the roadway did not match up with the report conclusions from Senior Sergeant Kuchenmeister.
Mr Hall said some of the tyre marks in Senior Sergeant Kuchenmeister's report did not exist, and others were not related to the crash.
He said modelling on a different program showed the teenager was driving either parallel to the highway's centre line, or on the correct side of the road.
The matter returns to court next Thursday.
