Updated at 5:45 p.m. with reaction from the victim's family and prosecutors.

A former Farmers Branch police officer was sentenced Tuesday to 10 years in prison for chasing down and killing a teenager he caught breaking into his SUV.

Ken Johnson, 37, was convicted of murder and aggravated assault in December for killing 16-year-old Jose Cruz and seriously wounding his friend in March 2016.

Ken Johnson was jailed Dec. 19 after he was convicted of murder and aggravated assault in the March 2016 killing of 16-year-old Jose Cruz. (Dallas County jail )

Johnson also received 10 years' probation for the aggravated assault, after the jury agreed that his actions constituted a crime of passion. He could be paroled after serving half of his sentence but would still face five years of probation after that. Johnson had faced up to life in prison.

Members of Cruz's family did not believe 10 years was enough for Johnson. They said they plan to fight to make sure he does not get paroled.

During a victim impact statement, Cruz's cousin pointed out that Johnson has two sons who must live with the verdict.

"Your sons will know that," Nora Rubi said. "They will not see you as the hero you were before."

She said Johnson would want a harsher sentence if his own family were the victims.

1 / 2Nora Rubi, 19, from left, Ana Cartagena, 13, Jose's sister, Norma Ochoa, grandmother of Jose Cruz, and Julio Cartagena, Jose's brother, console one another after former Farmers Branch police officer Ken Johnson was sentenced to 10 years in prison for the murder of Jose Cruz. Photo taken on Tuesday, January 9, 2018 at the Frank Crowley Courts building. (David Woo / Staff Photographer) 2 / 2Ana Henriquez, mother of Jose Cruz holds back tears after a 10-year sentenced was given to former Farmers Branch police officer Ken Johnson for the murder of Jose Cruz. The family said 10 years was not enough. Photo taken on Tuesday, January 9, 2018 at the Frank Crowley Courts building in Dallas. (David Woo/The Dallas Morning News) (David Woo / Staff Photographer)

Dallas County District Attorney Faith Johnson also questioned the former cop's sentence, saying he had violated his oath to protect and serve.

"We all believe a life is worth more than 10 years," she said.

Ken Johnson took the stand this week during the sentencing portion of his trial, saying Monday that he felt the evidence showed he fired in self-defense.

Johnson was off duty and in plain clothes when he chased down Cruz and Edgar Rodriguez after the two 16-year-olds broke into his Chevrolet Tahoe at his Farmers Branch apartment complex.

After stealing the third-row seats from his vehicle, the teens took off in a car, and Johnson chased them in his SUV.

After about a mile, Johnson rammed their car off the road, hopped out of his Tahoe and shot 16 times into the teens' car.

Jose Cruz was shot and killed in March 2016.

Cruz was killed, and Rodriguez was seriously wounded. Rodriguez testified in December that the teens didn't know Johnson was chasing them until moments before the crash.

Johnson said that he saw Cruz reach down after the crash, and that he believed the teen was grabbing a weapon. He testified Monday that he believed one of Cruz's wounds showed he was leaning down when Johnson fired.

"I just wanted to see his hands," Johnson said.

The teens were unarmed.

The shooting was one of many nationwide that have received public scrutiny about officers' use of fatal force.

Juries in Dallas County have been less inclined to convict police officers who have been charged with a crime. But Jason Hermus, the lead prosecutor in Johnson's murder trial, said he believes that's changing.

"Nationwide we're going through an evolution right now where juries are showing some change," he said, "some willingness to holding police officers, who do great misdeeds, holding them accountable."

Hermus also suspects that juries weighing the fates of police who commit crimes will be harsher with punishments in the future.

Despite her son's death, Ana Henriquez said she still respects law enforcement.

"We're just mad at one of the police officers, not all of them," she said Monday through an interpreter.

The family said they are still grieving Cruz's death and no longer celebrate holidays.

"It's like all our happiness is gone," Henriquez said.

Edgar Rodriguez was critically wounded in the same shooting. (Facebook)

Defense attorney Robert Rogers had insisted the shooting was a crime of passion, an argument that resonated with jurors.

"Consider his whole life," Rogers argued. "Thirty-seven years doing right, and he will be held accountable for those five seconds."

Johnson served in the U.S. Army. He said he enlisted to get out of his Oak Cliff neighborhood, where many of his friends were getting into trouble.

He served until July 2005, when he was honorably discharged. He then went to work for the Dallas Area Rapid Transit police department, where he worked before joining the Farmers Branch Police Department. He resigned from the force shortly after the deadly shooting.

"I've always wanted to help people," Johnson testified.

Several former and current DART officers who worked with Johnson described him as calm under pressure, and one said Johnson saved his life.

DART Officer Alfred Johnson said Ken Johnson, whom he calls "KJ," intervened after a man on a train attacked and tried to take Alfred Johnson's gun away.

Ken Johnson used pepper spray to incapacitate the man.

"He could've used deadly force on this individual, but he chose not to," Alfred Johnson said. "I thank him right now. ... Without him, I could've been killed."

Hermus argued that Johnson was full of "homicidal rage" the day he unloaded on the two unarmed teens.

He asked jurors to send a message to the community about what happens to police officers "who go astray."

Though Johnson said he was trying to arrest the teens because he believed they were connected to a string of car burglaries in the area, he admitted he was angry at them for taking his property.

"To be honest, I was a little angry," he said. "I was pretty upset."