The two managers of a bar in the Swiss Alps where at least 40 people died in a sudden fire early New Year’s Day have been placed under criminal investigation because of allegations of negligence, the police said on Saturday, as the authorities in Switzerland come under growing pressure to explain whether flaws in the site’s design and management fueled the disaster.

The investigation was opened on Friday night over suspicions of negligent homicide, negligent bodily harm and causing a fire by negligence, according to a statement from the police in the Valais canton, the area of Switzerland where the bar is.

The police statement did not detail what evidence had led to the criminal investigation, nor did it name the managers of the bar, called Le Constellation, in the center of Crans-Montana, a popular ski resort town in southern Switzerland.

Public business records identify the owners of the bar as a French couple, Jacques and Jessica Moretti, who opened it in 2015 after extensive renovations. Prosecutors did not immediately respond when asked to clarify whether the couple also managed the bar, but residents of Crans-Montana and local news media said they did.

As of Saturday, the Morettis had not responded to earlier requests for comment from The New York Times. In brief interviews with the Swiss media this week, they said they were fully cooperating with investigators and denied any wrongdoing.

“We can neither sleep nor eat; we are all in a terrible state,” Mr. Moretti told 20minutes.ch, a local news site.

In their statement, the police in Valais said that “the presumption of innocence applies until a final conviction is handed down.”

The Swiss president, Guy Parmelin, described the disaster as one of the worst tragedies in the country’s history. Many of the victims were seriously burned when the fire engulfed the bar’s basement, and the authorities have struggled to identify many of the dead as a result.

On Saturday, the police announced that they had identified eight more victims, all of them Swiss citizens aged 16 to 24, and they said that their bodies had been returned to their families. So far, though, only one victim has been publicly named: Emanuele Galeppini, a young Italian golfer.

Beatrice Pilloud, the prosecutor general of the Valais canton, said Friday that the likely cause of the fire had been the use of finger-size fireworks placed on bottles that sent up fountains of sparks, igniting foam insulation on the basement’s ceiling.

Ms. Pilloud told reporters in Crans-Montana on Saturday that the criminal investigation would allow the police to “explore all leads.”

Fire experts, witnesses and an analysis by The Times of visual evidence also suggest that the basement’s staircase exit became a deadly choke point, and it is unclear to what extent the building had been subject to required inspections. Ms. Pilloud said on Saturday that investigators were analyzing inspection documents that the Crans-Montana municipality had handed over.

“For me, it’s clear: something went wrong and someone made a mistake,” Stéphane Ganzer, an official in charge of security at the Valais canton, told SRF, a Swiss news media, on Saturday. “I’m certain of it.”

But asked on Saturday whether the tragedy could have been avoided, Beat Jans, the Swiss justice minister, said that “this is a question we cannot answer at the moment.”

“All the investigations are going on,” Mr. Jans said. “We will clarify the responsibilities.”