VANCOUVER—Police are working to determine the motive of a series of stabbings that left a woman dead and six others injured inside and around a public library in North Vancouver, B.C., on Saturday. Sgt. Frank Jang of the Integrated Homicide Investigation Team said a suspect in his 20s was in custody. The man has had interactions with police in the past and has a criminal record, he said. Jang said investigators still don’t understand the motive for the attack. “Obviously the question is why did this happen, I understand. We believe we know the how, the what, the where and the when. It is our job now to determine why,” he told a news conference near the library. “That is going to be the Number 1 question for us.” The attack wreaked havoc on a busy shopping area of North Vancouver early Saturday afternoon, where Jang said families had flocked …