The two managers of a bar where a blaze on New Year’s Day killed at least 40 people have been placed under criminal investigation, Swiss prosecutors have said.

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 about 1.30am local time (12.30am GMT) on Thursday, killing about 40 people and injuring more than 100.

The offences they are suspected of having committed are homicide by negligence, causing bodily harm by negligence and arson by negligence, the prosecutors’ office in the canton of Valais said in a statement on Saturday.

Investigators believe fountain sparklers mounted on champagne bottles and held too close to the ceiling caused the deadly fire.

One image circulating online on Friday appeared to show the ceiling of the basement where the new year’s party was being held, apparently clad with foam soundproofing panels, catching fire as the sparklers were held aloft.

“A criminal investigation was opened last night against the two managers of the bar,” police and the public prosecutor’s office in the south-western Swiss canton of Valais said. “They are charged with manslaughter by negligence, bodily harm by negligence and arson by negligence.”

The authorities said that “the presumption of innocence applies until a final conviction is handed down”.

Many of the injured were in their teens to mid-20s, police said. Authorities planned to look into whether the sound-dampening material on the ceiling conformed with regulations and whether the candles were permitted for use in the bar.

The process of identifying the dead and injured continued on Saturday as relatives waited, desperate for news.

Officials said they would also look at other safety measures on the premises, including fire extinguishers and escape routes. The region’s senior prosecutor has warned of possible prosecutions if any criminal liability is found.

The Valais region’s top security official, Stéphane Ganzer, told SRF public radio on Saturday that “such a huge accident with a fire in Switzerland means that something didn’t work – maybe the material, maybe the organisation on the spot”. He added: “Something didn’t work and someone made a mistake, I am sure of that.”

Nicolas Féraud, who heads the Crans-Montana municipality, told RTS radio he was convinced checks on the bar had not been lax, the broadcaster reported.