A Canadian teen who killed eight people in one of the country’s worst mass shootings frequented the same gory websites that American mass shooters have been known to visit leading up to attacks in the U.S., investigators found. Jesse Van Rootselaar opened fire on Feb. 10 at a home and a school in northeast British Columbia. The 18-year-old, who was born male and identified as a woman, left eight dead and dozens wounded before taking her own life. The attacks at Tumbler Ridge, about 700 miles north of Vancouver, are among the worst seen in America’s northern neighbor, where gun...