CALGARY, Alberta (AP) – A jury convicted a Canadian man Friday of helping his 12-year-old girlfriend kill her mother, father and younger brother, after her parents expressed disapproval over their relationship.

The panel deliberated about 11 hours before finding Jeremy Steinke, 25, guilty on three counts of first-degree murder.

The girlfriend, now 15, was earlier convicted on the same charges, making her the youngest Canadian ever to be found guilty in a multiple killing.

The girl, who is currently serving a 10-year sentence, cannot be named under Canada’s youth criminal laws.

According to testimony, Steinke helped the girl stab to death her parents because they disapproved of the 10-year age gap between the couple’s ages. Her 8-year-old brother was also killed.