Fired Balch Springs police officer Roy Oliver, who was convicted for the murder of 15-year-old Jordan Edwards, sits during the sentencing phase. Picture: Rose Baca/The Dallas Morning News via AP, Pool

Dallas - A former police officer was sentenced late Wednesday to 15 years in prison for fatally shooting an unarmed African-American teen as he left a house party in a Dallas suburb last year.

Roy Oliver, 38, could be eligible for parole after serving half of his sentence for the death of Jordan Edwards, a high school freshman lauded as a model student.

Jurors found the fired Balch Springs officer guilty of murder on Tuesday, an unusual outcome in most cases involving police shootings of civilians. Oliver, who is white, was escorted out of the courtroom in ankle shackles and spent the night behind bars in single-cell custody under constant supervision at the Dallas County Jail. He will continue to be isolated from other inmates "for his safety" until he is transferred to prison, a jail spokesman told The Washington Post.

"Roy's time in the penitentiary is going to be an excruciatingly long period of time," defense attorney Bob Gill had told the jury, asking them to sentence him to the minimum time allowed by state law.

The sentencing phase of the 10-day trial took an even more dramatic turn Wednesday when Wendy Oliver, the defendant's half-sister, took the stand. Her stepmother had asked jurors to go easy on him for the sake of his two young children, a request that prompted Wendy Oliver to message Jordan's stepmother and head to the courthouse to testify for the prosecution.

"I came here to do something right for Jordan Edwards," Wendy Oliver said on the stand. "It ate me up. Jordan didn't do anything to be shot."

She said she was close to her half-brother until she was 12, when their father, Roy Oliver Sr., was arrested and convicted of raping her. He spent 12 years in prison for the crime.

The former officer and his partner, Tyler Gross, were dispatched on April 29, 2017 to break up a house party after neighbours complained about drunken teens. Their visit started lightheartedly but became chaotic when members of an area gang fired shots into the air at a nearby parking lot, startling the youths at the party as well as the police.

Oliver claimed he was protecting Gross from a car that was reversing down the street when he fired an assault rifle five times into the vehicle. One of the gunshots struck Jordan, who was a passenger in the front seat. He died instantly.

The jury of 10 women and two men didn't buy Oliver's defense for the murder charge but acquitted him on two counts of aggravated assault with a deadly weapon by a peace officer.

Throughout the trial, jurors saw footage from the officers' body-worn cameras and heard from experts who disagreed over whether Oliver's use of force was justified. They also heard about an incident in which Oliver pulled out a gun after his truck was rear-ended weeks before the shooting, a Facebook post in which he bragged about being skilled at killing, and a psychological exam that an expert said raised red flags.

In closing arguments, Dallas County District Attorney Faith Johnson described Oliver as "a killer in blue."

Oliver is the first officer in the country to be convicted of murder in an on-duty shooting since 2005, according to Philip Stinson, a criminologist at Bowling Green State University who tracks police misconduct. Earlier this year, a Dallas County jury convicted Ken Johnson, a former area officer, of murder and aggravated assault and sentenced him to 10 years in prison for shooting two teenagers, one fatally, while off-duty.

"This verdict America needed so we can understand that all lives matter," said Martin Lee Dorsey, the Edwards's family pastor.

The jury, which deliberated more than five hours, also sentenced Oliver to pay a $10 000 fine.

The Washington Post