(CNN) A Texas jury sentenced a former police officer to 15 years in prison Wednesday night for the shooting death of an unarmed African-American teen in a Dallas suburb.

The jury deliberated for 12 hours before deciding the fate of former Balch Springs officer Roy Oliver. In addition to the prison term, it imposed a fine of $10,000.

Oliver was convicted of murder Tuesday by the same jury for the killing of high school freshman Jordan Edwards, 15. He fired into a car full of teens on April 29 last year, saying he believed it was moving aggressively toward his partner.

Dallas County District Attorney Faith Johnson described Oliver as a "killer in blue" who violated his oath to protect citizens. Prosecutors sought a sentence of at least 60 years while the defense argued for 20 years or less.

Johnson said she wished Oliver's sentence was much longer, but she respected the jury's decision and realizes a guilty verdict for an officer is rare in police shootings.

Charmaine Edwards said she would have preferred a sentence of 25 to 30 years for the killer of the stepson she raised.

"He actually can see life again after 15 years," she said. "And that's not enough because Jordan can't see life again."

'This case is not just about Jordan'

A day before the sentencing, the rare guilty verdict in the trial of a police officer prompted gasps and sobs in the courtroom.

Few police officers face trial in shooting deaths, and even fewer are convicted. Most police-involved shooting deaths, including Philando Castile's in Minnesota and Alton Sterling's in Louisiana , have ended in acquittals or no charges despite national protests condemning police brutality.

"We don't want another parent to have to go through what this family has had to deal with," Jordan's family attorney, Daryl Washington, said. "This case is not just about Jordan. It's about Tamir Rice. It's about Walter Scott. It's about Alton Sterling. It's about every African-American ... who have been killed and who have not gotten justice."

Private party turns deadly

Jordan's family said he was at a private party with his two brothers and two friends when someone announced that police had been dispatched. The group headed to the car.

Around 11 p.m., Oliver and another officer responded to the home after reports of underage drinking. While in the residence searching for the homeowner, they heard what they believed were gunshots nearby, police said.

One officer went to the area where he heard the gunshots, and Oliver went to his squad car and retrieved his patrol rifle, according to an arrest warrant by the Dallas County Sheriff's Office.

The officer who was with Oliver saw a Chevrolet Impala reversing and repeatedly ordered it to stop. He then approached the vehicle from the passenger side with his weapon drawn, police said.

The vehicle stopped, then slowly moved forward as the officer punched the passenger door window, breaking it, the arrest warrant said.

Oliver discharged multiple rounds from his patrol rifle as the vehicle drove past him, the arrest warrant said. One bullet struck Jordan, who was a passenger in the car.

Jordan's father said neither the teen nor his group posed a threat to the officers' safety.

Defense: Officer had to make a quick decision

During closing arguments, Johnson described the teen as a model student -- hardworking, smart and always smiling.

"He was a great athlete, football player, student," she said. ""This man right here, Roy Oliver, took his life. He's a police officer that we trusted to protect us, to keep us safe."

Roy Oliver

Defense attorney Bob Gill said there was no question Jordan was an exceptional teen. However, he said, Oliver had to make a split-second decision to protect his partner.

"He did not know who Jordan was. His loyalty and fidelity to his partner caused him to act," Gill said.

After the shooting, Balch Springs Police Chief Jonathan Haber initially said the car Jordan was riding in was moving aggressively toward police -- leading Oliver to fire his rifle.

But days later, Haber said he misspoke, adding that body camera footage showed the car was driving forward, away from the officers -- not reversing toward them. Haber fired Oliver shortly afterward.

The jury convicted Oliver of murder, but found him not guilty of two lesser charges of aggravated assault and manslaughter. His legal team said it plans to appeal the verdict, CNN affiliate KTVT said.

Body cameras played a crucial role

Police body camera footage played a crucial role in the conviction.

Calls for police body cameras have grown as incidents of police brutality make headlines nationwide, with dozens of major police departments using them to provide transparency and accountability.

Jordan's shooting was one of several recent deaths of African-American men at the hands of police, which have sparked national protests and a debate on police conduct.

Convictions such as Oliver's are rare mostly because when an officer says the person flashed a gun or made a sudden move, jurors tend to side with them, said Kristen Clarke, president and executive director of the Lawyers' Committee for Civil Rights Under Law.

"At the end of day, officers in their badge and uniform enjoy the benefit of the doubt," Clarke said last year.