HALIFAX—When a gunman impersonating a Mountie started killing people in Portapique, N.S., on April 18, 2020, four children huddled in a home where they relayed key information about the killer as the tragedy unfolded around them. Portions of a transcript of that disturbing 911 call were released today by an independent commission of inquiry investigating the worst mass shooting in modern Canadian history, which claimed 22 lives over a 13-hour span. The phone conversation is recounted in a 90-page document that focuses on the first hour of the killer’s rampage. It offers clear evidence that authorities were told about the shooter’s identity and his replica police vehicle before he used a back road to evade a police blockade. Recordings of the 911 calls were not played during the hearings. However, the so-called foundational document provides grim, detailed descriptions of how 13 people were gunned down that night, including Gabriel Wortman’s …