A FATHER whose teenage son was shot dead by police after he called 911 to teach the boy a lesson for stealing his truck has revealed his heartbreak.

James Comstock said his son Tyler Comstock, 19, took his vehicle without permission before he was killed on Monday.

"He took off with my truck. I call the police, and they kill him," Comstock, from Iowa in the United States, told The Des Moines Register.

"It was over a damn pack of cigarettes. I wouldn’t buy him none. I lose my son for that."

Police pursued Tyler as he drove around a crowded Iowa State University campus, before ramming patrol officer Adam McPherson's car.

Once the truck stopped, the teenager refused to cut the engine.

Students dived for cover as the officer fired six shots into the truck.

Tyler was rushed to hospital but died from two gunshot wounds to his head and chest.

Mr Comstock said he’s outraged police shot and killed his unarmed son.

During the chase, an unidentified Ames police staffer twice suggested that police back off their pursuit.

Tyler Comstock’s step-grandfather Gary Shepley, 65, said "hard, tough questions" need to be asked about the police’s actions.

Tyler's family said the young man had made mistakes, but was taking steps to get his life back on track after breaking up with his girlfriend.

He had spent several days in jail because of a disorderly conduct charge, the family said.

"He called me every night, trying to straighten his life out," father James Comstock said. “He was a smart kid. He made his own computers. He was interested in IT."

Shari Comstock, Tyler’s mother, was left with more questions after hearing the dispatcher audio.

"I just heard the audio of the dispatch. They told (police) to back off," she said.

"Why? Why did they kill him? I don’t understand why this happened. Tyler would never hurt anybody. He was just a scared child."

Police are investigating.

Read more at The Des Moines Register.