This post has been updated.

DALLAS — A former police officer was sentenced late Wednesday to 15 years in prison for fatally shooting an unarmed African American teen leaving 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, a rare outcome in cases involving police shootings of civilians. Oliver, who is white, was escorted out of the courtroom in ankle shackles and spent the night 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.

“We feel very comfortable about the verdict,” Dallas County District Attorney Faith Johnson said after sentencing. Jordan’s stepmother, Charmaine Edwards, said the family was thankful. “Although we wanted more years, this is a start for us,” she noted.

Oliver’s attorneys signaled they would appeal. “We believe there were some significant errors made during the trial,” defense attorney Bob Gill said.

The second phase of the 10-day trial took a 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 neighbors 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 driving away when he fired an assault rifle five times into the vehicle. One of the gunshots struck Jordan, 15, 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 the prosecution’s closing arguments, Johnson described Oliver as “a killer in blue.” After sentencing, she issued a more encompassing statement: “We love the police; however, we do not support bad apples.”

Oliver is the second officer since 2005 convicted of murder resulting from an on-duty shooting, according to Philip Stinson, a criminologist at Bowling Green State University who tracks police misconduct. James Ashby of the Rocky Ford Police Department in Colorado was charged in 2014 and convicted in 2016, sentenced to 16 years in prison.

“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.

Correction: A previous version of this post incorrectly said that Roy Oliver is the first police officer since 2005 convicted of murder resulting from an on-duty shooting. He is the second.