The mysterious crash of CP Flight 21 five decades ago remains one of the largest unsolved mass murders in Canadian history. The commercial flight took off from Vancouver, bound for Whitehorse on July 8, 1965, when it exploded in mid-air over the B.C interior. All 52 people on board were killed. Weather was ruled out as a factor. The investigation quickly determined it was a criminal act and that a bomb had been planted in the airplane's rear lavatory. The RCMP identified four persons of interest, but were never able to determine who was responsible. As a result, no charges were ever laid and the case was closed. In 2018, CBC News journalists began their own investigation, combing through evidence and interviewing dozens of people connected to the crash. Specialists in various fields were brought in to review the evidence. Here is what we learned.