A boy, who was 14 at the time, shot and killed his mother and five-year-old sister in this farmhouse in 2007. (CBC)A 17-year-old Manitoba boy has been handed the maximum youth sentence of seven years after pleading guilty to shooting his mother and five-year-old sister to death in a rural farmhouse in August 2007.

The teen, who was 14 at the time of the killings, cannot be identified under provisions of the Youth Criminal Justice Act.

A Brandon judge handed the youth an additional seven years on top of the almost three years he has spent in custody, following the teen's guilty plea to two counts of second degree murder earlier this year. Under the Youth Criminal Justice Act, after serving four more years in custody, the teen becomes eligible for supervised community release that would continue for another three years.

The teen offered no reason for the killings to police or psychiatrists. He alleged he was abused and sometimes beaten by his adoptive mother, who allegedly threatened to kill him or beat him. He expressed remorse for the death of his five-year-old sister.

On Wednesday, Justice Robert Cummings of Manitoba's Court of Queen's Bench had to choose between giving the teen a youth sentence or an adult sentence, the latter requiring a mandatory term of life in prison. In a written decision, Cummings said he chose the maximum youth sentence because all the expert testimony suggested the boy's best chances for counseling and rehabilitation would come with a youth sentence.

The judge noted the teen had no prior involvement with the law. "His personality and development have been adversely affected by his upbringing," the judge said, noting there was evidence the mother had said she hated the boy and that his relationship with her was "poor."

The bodies of the teen's 43-year-old mother and little sister were discovered by the woman's husband. The shootings rocked the small community of St. Lazare, about 300 kilometres west of Winnipeg.

The teen went through an extensive pre-trial process that involved psychiatric evaluations and other assessments.