Until three years ago, a mandatory life sentence would have been waiting for the young Harvey man convicted of killing Harry “Mike” Ainsworth in an Algiers Point slaying that became widely known as the “Good Samaritan murder.”

But a mandate handed down by the U.S. Supreme Court five months after the 2012 shooting has forced Louisiana judges to consider sparing youthful offenders the finality of life in prison without parole, and it left Orleans Parish Criminal District Court Judge Darryl Derbigny with a decision: how to weigh what the high court called a child’s “diminished culpability and heightened capacity for change” against the loss of a father gunned down in front of his two young sons as he tried to halt a carjacking on a quiet winter morning.

On Friday, Derbigny chose to spare 21-year-old Kendall Harrison a guaranteed life prison sentence, granting him the chance of parole after 45 years.

A jury late last year convicted Harrison of second-degree murder and armed robbery with a firearm. Harrison was six months shy of his 18th birthday when he shot Ainsworth through the windshield of a Saturn Ion that he was trying to steal.

Ainsworth, a 44-year-old handyman who had sprinted toward the robbery in progress while walking his two boys to the bus stop on the morning of Jan. 25, 2012, was hit twice. His sons, then ages 9 and 11, witnessed the shooting.

Five months later, in Miller v. Alabama, a 5-4 Supreme Court majority outlawed automatic life sentences without parole for those who were under 18 when the crime took place. The court said that “youth matters for the purposes of meting out the law’s most serious punishments,” and that judges must first weigh a defendant’s age before denying him a shot at eventual release.

The court majority reasoned that “appropriate occasions for sentencing juveniles to this harshest possible penalty will be uncommon.”

Derbigny held a required hearing in July in which Harrison took the witness stand and fielded direct questions from Ainsworth’s loved ones, repeatedly claiming he was falsely convicted. The judge also ordered a report from state parole officials, who recommended life without parole for Harrison.

The judge decided differently, though he chastised Harrison on Friday.

“You brutally and callously took the life of Harry ‘Mike’ Ainsworth. When you did that, you took a husband from his wife. You took a son from his mother. You took a father from his son. You took a friend and worthy asset of Algiers, a proud community,” Derbigny said as Harrison stood before him in orange jail scrubs.

“You sat on the witness stand and did not display a single iota of remorse for the heinous and senseless killing for which you were convicted. By your hateful actions you have instilled fear in both the Ainsworth family and the entire community.”

Referring to both Ainsworth’s and Harrison’s families, Derbigny added, “You have visited an eternal plague on both houses.”

Christopher Bowman, a spokesman for District Attorney Leon Cannizzaro’s office, said it was just the second time since the Supreme Court ruling that a Criminal District Court judge has handed an eligible juvenile convict less than mandatory life.

Retired Judge Calvin Johnson, serving ad hoc, did the same thing for Steven Williams, who was convicted of murder in 2013. Johnson sentenced Williams to life, but with the possibility of parole. Williams too was 17 when he murdered 24-year-old DeMarcus Jordan in 2006.

Harrison’s arrest in the Good Samaritan case came as a result of Crimestoppers tips and DNA evidence that helped cement his conviction.

Ainsworth heard screams and ran from the bus stop to the carjacking site at 7 a.m. He leaped onto the Saturn and bashed the windshield with his arms and fists before the carjacker, who had made his way into the driver’s seat of Anita Hedgepeth’s vehicle, fired a 9mm handgun, according to trial testimony.

Harrison told detectives later he was in Harvey at the time and hadn’t been in Algiers Point for more than a week before Ainsworth was shot. But a pair of relatives testified that he was with them, three blocks away. A cousin said Harrison showed up about 7:30 a.m. as police converged on the crime scene.

Other witnesses reported the shooter took a circuitous route from the crime scene in the 500 block of Vallette Street to the 800 block of Vallette, where the relatives said Harrison turned up.

After Friday’s sentencing, Hedgepeth, the carjacking victim, said she was relieved and satisfied with the 45-year minimum sentence for Harrison, though she would have preferred that he stay behind bars forever.

“I feel it’s just,” she said of the sentence. “I’m glad it’s over.”

Attorney Lionel “Lon” Burns, who has represented Harrison, said Derbigny “had mercy on him.”

“Everything else is stacked against him,” Burns said of his client. “It provides the guy with some hope.”

Cannizzaro did not respond to a request for comment.

Follow John Simerman on Twitter, @johnsimerman.