The southern Alberta teen accused of shooting a German tourist in the head while driving on a highway west of the city has been found guilty of aggravated assault and recklessly discharging a firearm.

"I find the Crown has proven [the boy] was the shooter," provincial court Judge George Gaschler said on Friday morning.

The teen from the Stoney Nakoda First Nation cannot be identified because he was 16 at the time.

During the trial, Gaschler heard evidence that Horst Stewin and his family were in Alberta to celebrate his 60th birthday in August 2018.

The family was driving near the Morley rodeo grounds about 55 kilometres west of Calgary when a car full of young people from the nearby Morley reserve pulled up beside the family's SUV.

This is the gun police say was used to shoot Horst Stewin, who was driving on the highway west of Calgary in August 2018. The gun was buried in a wooded area by one of the people who had been in the vehicle with the shooter. (Court exhibit)

The teen opened fire, shooting Stewin in the head and causing the SUV to veer off the highway and crash into a tree.

During the trial, there was evidence the boy confessed to the shooting to a friend in Facebook messages.

Other key evidence included the testimony of eyewitnesses — other young people from Morley who were in the same car as the shooter and identified the teen as the one who pulled the trigger.

"I find that the three witnesses ... each in their own way and each from their own position and perspective identify [the teen] as the shooter," Gaschler wrote in his decision.

But defence lawyer Balfour Der said he was expecting an acquittal based on those witnesses.

"I'm actually quite disappointed," said Der after the decision was handed down.

"I thought there was plenty of reasonable doubt in this case based primarily on the quality of these witnesses the prosecution called. After cross-examination I don't know you could have believed anything they said."

These eight bullet fragments were removed from Horst Stewin's brain by German doctors three weeks after he was shot while driving west of Calgary. (Court Exhibit)

Stewin survived and was eventually flown back to Germany, where doctors removed eight bullet fragments from his brain.

The 61-year old has still not fully recovered and will suffer lifelong injuries.

He is paralyzed on his right side, has trouble speaking and likely will never work again.

A sentencing hearing will take place in February.

Der said he is considering an appeal.

The boy will turn 18 in two weeks. He smiled at two family members, including his grandmother, who were in court Friday for the decision.