Investigators are racing to establish how and why the deadly New Year's Eve fire at a bar in a Swiss ski resort spread so rapidly.
Authorities on Friday said in a press conference that sparklers attached to champagne bottles that were held too close to the ceiling appear to have started the blaze in the basement of Le Constellation bar in Crans-Montana.
But how the fire took hold with such ferocity, killing at least 40 people and leaving 119 injured, many seriously, is now a key focus for officials - as is the bar's safety record.
BBC Verify has been examining videos taken by survivors and onlookers and speaking to fire safety experts to find clues about what went wrong.
Bottles with sparklers held in the air
Two striking images shared widely online show people carrying champagne bottles with lit sparklers above their heads, with a crowd around them.
One image shows flames starting to gather on the ceiling above people holding five of these bottles aloft.
The second image shows a person wearing a crash helmet and holding a bottle with a lit sparkler, sitting on the shoulders of another person wearing a Guy Fawkes mask. The sparks from this bottle appear to be closer to the ceiling.
BBC Verify determined these images were taken after midnight on 1 January by confirming there were not earlier versions and matched them against public photos of Le Constellation - using details including the bar design and distinctive pipework.
And there was no evidence the images had been manipulated using artificial intelligence (AI).
To sum up, the fire and investigation lead to serious questions about the safety measures in place for such events. As the authorities seek answers, stories of survivors and the tragedy itself remain vivid reminders of the potential dangers present in seemingly festive settings.
