An Iowa teenager who shot and killed two fellow students at an alternative school program for at-risk youths last year and wounded the program’s founder was sentenced on Thursday to 65 years in prison, prosecutors announced.

The teenager, Preston Walls, 19, of West Des Moines, was convicted in September of second-degree murder, voluntary manslaughter and assault causing serious injury in connection with the attack on Jan. 23, 2023, in what the authorities called a gang-related shooting.

Judge Larry McLellan of the Polk County District Court sentenced Mr. Walls to three consecutive prison terms, one for each charge, totaling 65 years, according to prosecutors. He was also ordered to pay $150,000 in restitution to the slain victims’ families, the Polk County Attorney’s Office said in a news release. Mr. Walls will be eligible for parole after 40 years, prosecutors said.

The authorities said at the time of the shooting that Mr. Walls was in a gang and that the two teenagers he fatally shot, Rashard Carr, 16, and Gionni Dameron, 18, were members of an opposing gang. All three were students at the program and knew each other, The Des Moines Register reported.

During the trial, Mr. Walls testified in court that he had shot Mr. Carr and Mr. Dameron because he feared for his life. Mr. Walls said that he had “acted out of fear” and had “felt like they were going to kill me.”

At sentencing, Mr. Walls told the victims’ families that was “truly sorry,” but he reiterated that he had feared for his life, prosecutors said. His mother and other relatives also testified about events that had shaped Mr. Walls’s life, including the death of his father.

The victims’ mothers read victim impact statements, prosecutors said, stating that their sons wouldn’t have hurt Mr. Walls, and that in some cases, they had stood up for him.

William Holmes, 50, the sole survivor of the shooting and the founder of Starts Right Here, the alternative school program, also delivered a final message to his former student, prosecutors said.

“I wanted to be there for you,” Mr. Holmes told Mr. Walls in court, according to the news release. “I had your back like there was no tomorrow, and you know that.”

“Why did you choose the place you love to do something like this?” he added.

A call to Mr. Walls’s lawyer, Glen Downey, was not immediately returned on Thursday night. The defense had requested that the sentences Mr. Walls received run concurrently.

The Polk County Attorney’s Office did not immediately return phone and email messages.

On the afternoon Jan. 23, 2023, Mr. Walls showed up at Starts Right Here in Des Moines, carrying a handgun and an extended ammunition magazine, according to the authorities. He encountered Mr. Holmes, who tried to escort him out of the area, the authorities said.

Mr. Walls shot Mr. Holmes and then the two students before running away, the authorities said. Mr. Holmes suffered injuries to his hip and finger, prosecutors said.