French couple Jacques and Jessica Moretti owned and managed the Le Constellation Bar in Crans-Montana, which was crammed with young New Year’s revellers when a blaze began at around 1:30 am (0030 GMT) on Thursday.
Forty people were killed and 119 injured, most of them seriously, according to the latest toll.
“A criminal investigation was opened last night against the two managers of the bar,” police and the public prosecutor’s office in the southwestern Swiss canton of Wallis said in a statement.
“They are charged with manslaughter by negligence, bodily harm by negligence and arson by negligence.”
The authorities recalled that “the presumption of innocence applies until a final conviction is handed down”.
The question of whether safety standards were respected has been debated ever since the devastating blaze.
Jacques Moretti insisted to the Swiss press on Friday that all safety norms were followed at the bar, which according to the Crans-Montana website had a capacity of 300 people plus 40 on its terrace.
But the chief prosecutor of the Wallis region, Beatrice Pilloud, said that the standards were among the focuses of the investigation.
She told reporters Friday that the leading hypothesis was that “sparklers or Bengal candles attached to champagne bottles and lifted too close to the ceiling” had ignited the deadly fire.
Videos shared on social media showed the low wooden ceiling -- covered with soundproofing foam -- catching alight and the flames spreading quickly, as revellers continued to dance, unaware of the death trap they were in.
Several witnesses said the event space in the basement of the establishment, where the fire began, was connected with the ground floor by only a staircase, which some described as “narrow”.
