A fire that ripped through a nightclub in the Swiss Alps early New Year's day has killed at least 40 people. Swiss authorities said that champagne sparklers were the likely cause. CNN's Nic Robertson breaks down the sequence of events that led to this tragedy. https://cnn.it/44S4rUV | CNN

Videos verified by CNN show the initial moments of the deadly fire at Le Constellation bar in Crans-Montana, Switzerland. About 40 people were killed and more than 100 people were injured in the blaze on New Year's Day. Follow live updates here: https://cnn.it/4qaMidK | CNN