Jacques Moretti, co-owner of the Swiss bar which went up in flames during New Year celebrations, has been detained in Sion due to a potential flight risk, local media reported.
Mr Moretti and his wife Jessica, who co-own Le Constellation bar in the ski-resort of Crans-Montana, were interviewed by prosecutors in the Switzerland's southwestern Wallis canton.
The fire killed 40 people and injured 116 others. The average age of those killed was 19.
Ms Moretti said today that her thoughts were constantly with the victims and that she would like to apologise to the victims and all those "still struggling".
Switzerland today held a nationwide minute of silence to remember the victims of the deadly fire.
The silence was followed by church bells across the country ringing for five minutes, at the start of a national ceremony of remembrance.
The moment of silence stood as a "testament to the shared grief felt by the entire nation with all the families and friends directly affected", the Swiss government said in a statement.
At the same time, a memorial ceremony for the victims was held in Martigny, a town about 50km down the valley from Crans-Montana, which had been rendered all but inaccessible by a large snowstorm.
Inhabitants of the ski resort town were able to watch the ceremony as it was livestreamed to large screens, including at the congress centre that for days after the tragedy accommodated families seeking news of missing loved ones.
Swiss President Guy Parmelin, who has declared the fire "one of the worst tragedies that our country has experienced", was joined for the ceremony by his French and Italian counterparts, whose countries lost nine and six nationals respectively in the fire.
Top officials from Belgium, Luxembourg, Serbia and the European Union also participated in the ceremony.
Most of those impacted by the inferno at Le Constellation were Swiss, but a total of 19 nationalities were among the fatalities and the wounded.
Half of those killed in the blaze were under 18, including some as young as 14.
Of those injured, 83 remain in hospital, with the most severely burned airlifted to specialist centres across Switzerland and abroad.
Prosecutors believe the blaze started when champagne bottles with sparklers attached were raised too close to sound insulation foam on the ceiling in the bar's basement section.
Experts have suggested that what appeared to be highly flammable foam may have caused a so-called flashover - a near-simultaneous ignition of everything in an enclosed space, trapping many of the young patrons.
Video footage from the scene showed young people desperately trying to flee the scene, some breaking windows to try to force their way out.
On Tuesday, municipal authorities acknowledged that no fire safety inspections had been conducted at Le Constellation since 2019, prompting outrage.
The investigation under way will seek to shed light on the responsibilities of the authorities, but also of bar owners Jacques and Jessica Moretti.
The French couple are facing charges of manslaughter by negligence, bodily harm by negligence and arson by negligence.
The pair said in a statement that they were "devastated and overwhelmed with grief", and pledged their "full cooperation" with investigators.
They will need to answer numerous questions about why so many minors were in the bar, and whether fire safety standards were adhered to.
There has been much focus on the soundproofing foam, which, according to photos taken by the owners, had been added during renovations in 2015.
A video filmed by a member of the public, screened on Monday by Swiss broadcaster RTS, showed that the danger was known years ago.
"Watch out for the foam!", a bar employee said during 2019 New Year's Eve celebrations, as champagne bottles with sparklers were brought out.
"This video is staggering," Romain Jordan, a lawyer representing several affected families, said, adding it showed "there was an awareness of this risk - and that possibly this risk was accepted".
