On Thursday the local prosecutor in Grenoble Jean-Yves Coquillat briefed the media about the fatal avalanche, that left two pupils dead as well as a Ukrainian man.
The prosecutor confirmed that the teacher had been formally placed in custody although he remains in hospital after being knocked unconscious in the avalanche at the Deux Alpes resort.
Without giving many details of the reason to place the teacher in custody, Coquillat said “it was difficult to question him unless they forced it”.
Since news of Wednesday's tragedy broke questions have been raised about the actions of the teacher and why the pupils were skiing on a black level slope – the most difficult level – when it was not open to the public.
But despite being questioned for possible multiple manslaughter the prosecutor warned against passing judgement on the teacher.
“I remind you that this teacher benefits from the presumption of innocence,” he said. "This type of disaster is a result of chain of events that needs to be defined.
“It needs to be remembered that skiing off-piste is not a crime and it's not forbidden,” he added.
The prosecutor also confirmed that the ski run had been closed to the public since the start of the season because of a lack of snow. The presence of rocks on the slope had made it too dangerous to open.
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Netting had been placed across the ski run and as well as signs to say it was closed, but this was ignored by the school party.
A Romanian national also admitted to police that they were among a separate group of 15 skiers who were skiing above the school party on the same slope when the avalanche was triggered.
It is unclear whether this group may have triggered the avalanche that swept away the school party.