A criminal investigation was launched yesterday into the French owners of the Swiss ski bar engulfed by a deadly inferno on New Year's Eve, amid claims that an emergency exit at the venue was 'always locked'.

Police announced that Jacques Moretti, 49, and his wife Jessica, 40, were being investigated on suspicion of manslaughter by negligence, bodily harm and arson after a horrific blaze killed 40 and injured 119.

The inferno at Le Constellation in the Alpine resort of Crans–Montana erupted in the venue's basement bar when sparklers in champagne bottles set a ceiling covered in insulation foam alight.

Harrowing video footage showed revellers, many of whom were teenagers, continuing to party as the flames spread across the ceiling, losing crucial seconds during which they could have fled.

The venue was branded a 'deathtrap' after it emerged that partygoers squeezed up a narrow staircase to escape the flames and toxic smoke in the basement.

But in a major development, it was yesterday claimed there was another potential escape route via an emergency exit within the basement – but that it was allegedly always locked.

Andrea, 31, a bartender who works elsewhere in the resort but was a regular at Le Constellation, told German newspaper Bild: 'There was an entrance that also served as an exit. And there was an emergency exit. But whenever I was there, it was always locked.

'Everyone in town knew things were bound to go wrong eventually.

'The emergency exit was in a separate smoking room. Hardly anyone used it; most went up to the conservatory. The smoking room was used as a kind of storage room. There was a sofa inside in front of the door, and carelessly discarded objects lay outside.'

Pictured: 16–year–old girl Chiara Costanzo, from Milan, Italy, was the second person to be named as a victim

A makeshift memorial outside the 'Le Constellation' bar following the fire 

Another witness, Grigori, who was on his way to the bar when the fire erupted, and whose friend is among the missing, said: 'There's another exit, but I think they were locking it because some people were escaping without paying.'

The Mail on Sunday has also identified a third exit on the ground floor of the bar, which led into a covered shopping area that includes a ski rental shop. 

Anyone using that exit would then, however, have to go through another glass door to escape on to the street. It is unclear whether either of those doors were open or locked when the fire started at 1.30am.

The revelations came as a 16–year–old girl from Milan, Italy, was the second person to be named as a victim. Chiara Costanzo's father, Andrea, told an Italian newspaper he felt a 'great emptiness' after receiving a call 'that should never come to a father'.