After shooting a German tourist in the head in what might have been a case of mistaken identity, the 16-year-old shooter yelled, "We caught a body," one witness said during his testimony at the boy's trial in Calgary.

A 17-year-old boy is on trial, facing charges of aggravated assault, assault, and three firearms-related offences. His identity is protected by a publication ban under the Youth Criminal Justice Act.

Horst Stewin, 61, is paralyzed on his right side and still has trouble speaking after eight bullet fragments were removed from his brain last summer, 20 days after he was shot while driving on Highway 1A west of Calgary.

"His prognosis for a full recovery is guarded at best," Crown prosecutor Dane Rolfe said in laying out an agreed statement of facts at the beginning of the teen's trial Monday morning.

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

Stewin has had to learn to write with his left hand, is often confused and has memory issues, according to Rolfe. The prosecutor also said the victim has trouble speaking and is in physical therapy three times a week.

Several months ago, a charge of attempted murder was dropped by the Crown after prosecutors decided there was no reasonable likelihood of conviction.

The Crown's first witness was a young woman who lives in the Morley, Alta., First Nations settlement, about 60 kilometres west of Calgary. She said she was in the car on Aug. 2, 2018, when the teen shot the tourist.

CBC News is calling the witness L, because of the risk that naming her could identify the accused.

Based on cross-examination questions from defence lawyer Balfour Der, the driver of the car carrying young people from the Morley community believed the person in the black SUV was a man who had attacked his brother.

The rented SUV driven by Horst Stewin veered off the road and hit a tree. (Court exhibit)

L testified she was in the back seat of her friend's car as it drove west on Highway 1A.

She said the driver ordered the accused to shoot, and he "did it."

"I just shut my eyes and covered myself," said L. "Would you want to see someone shooting somebody?" she asked the prosecutor.

Driver in custody on unrelated matter

The driver of the car also testified, telling the judge the boy shot Stewin. "He was telling us, 'We caught a body, we caught a body.'"

Under cross-examination, the witness admitted to Der that he had initially lied to police as they investigated the shooting.

The car's driver, who is in custody on an unrelated charge, testified that he and his three passengers had been drinking vodka and smoking meth when he saw the black SUV and sped up to pass it.

"As I was passing the vehicle I heard the bang. It was the .22. It came from the back seat. I saw him sit down. I looked in the rear-view mirror and the black SUV hit the ditch," he said.

The driver, now 25, said he liked the suspect who he described as "some kid hanging around us older dudes." He testified he had been trying to be a big brother to him.

"Did you know he was going to shoot?" asked Rolfe. "No," the driver replied. "Did you tell him to shoot it?" Rolfe asked. "No."

The driver of the car the youth was in also testified that he kept hold of the rifle used in the shooting and wasn't going to take the blame for the shooting. "I wasn't going to go down for that," he said.

In cross-examination, Der pointed out that the witness had lied to police on several occasions and had been high on alcohol and meth, so his memory of the day is likely to be suspect.

"Really we can't trust anything you're telling us because your mind was clouded by drugs and alcohol, correct?" Der asked.

The driver admitted that he and a friend had gone to the 16-year-old's home before any arrest and beat him up. He didn't explain why.

This gun was buried in a wooded area by one of the people who had been in the vehicle with the accused. (Court exhibit)

Birthday celebration

Stewin, his wife, his son and his son's girlfriend were in Canada celebrating his 60th birthday when he was shot.

The family had stopped to take photos near the Morley rodeo grounds, about 55 kilometres west of Calgary. As they pulled back onto Highway 1A, their black SUV was overtaken by another vehicle.

As the car pulled up beside the family, Stewin — who was driving — was shot once in the head, causing him to veer off into a ditch and crash into a tree.

Stewin was airlifted to hospital but the bullet could not be safely removed from his head.

After a two-week stay, the victim was flown back to Germany, where doctors successfully removed the fragments.

The accused was arrested on the Stoney Nakoda First Nation west of Calgary about three weeks after the shooting.

Last year, the teen was released on bail but breached his release conditions and was re-arrested.

He is currently in custody.

Provincial court Judge George Gaschler is presiding over the seven-day trial.