The teen who killed four people and wounded seven others in a mass shooting in La Loche, Sask., apologized in court on Tuesday as he was handed a life sentence in prison with no parole eligibility for 10 years.

The killer, who was 17 at the time of the shooting, was sentenced as an adult after a judge decided a youth sentence would not be appropriate. He cannot be given consecutive sentences due to his age at the time of the incident.

"I can't undo what I did. I'm sorry," the shooter said in court.

He pleaded guilty to two counts of first-degree murder, two counts of second-degree murder and seven counts of attempted murder in October 2016. ​He still cannot be named until an appeal period lapses.

He fatally shot 35-year-old teacher Adam Wood, 21-year-old teacher's assistant Marie Janvier, and teenagers Drayden and Dayne Fontaine, and wounded seven other people.

There are more than 24 community members the shooter was ordered not to contact. He is also prohibited from owning firearms for life.

Judge Janet McIvor described the shooter's actions as "senseless" and "calculated to inflict the maximum possible damage."

Aaron Fox said his client needs help, and the shooter has repeatedly asked himself 'why, why why?' (Jason Franson/Canadian Press)

"The violence was unprovoked and it was gratuitous," McIvor said, noting that the entire community of La Loche was victimized by the shootings.

The shooter's lawyer, Aaron Fox, made a case for the sentence to be served in a psychiatric centre. Though McIvor agreed that serving his sentence in a psychiatric facility would be "good" for the shooter, she sentenced him to a term in a federal penitentiary.

Fox said his client needs help and the shooter has repeatedly asked himself "why, why why?" The shooter's only therapy sessions have been the times when he talks with the chaplain in the Prince Albert penitentiary.

Fox said the only insight into the shooting will come from the shooter, if he's given therapy and treatment in a psychiatric centre.

"[The shooter] has a very, very, very long road ahead of him" McIvor said.