Four more current and former officials are now under criminal investigation in the probe into Switzerland's Crans-Montana fire disaster, sources close to the case have said.
"The investigation has been extended to include four new individuals, bringing the total number of defendants to 13," the public prosecutors' office in southwest Switzerland's Wallis canton confirmed to AFP.
The Crans-Montana municipal councillor in charge of security, their 2013-2016 predecessor, the current deputy head of the public safety department, and the 2009-2016 mayor of the neighbouring municipality of Chermignon, will be interviewed between 11 May and 3 June, sources close to the case added.
The fire in a bar in the Swiss ski resort of Crans-Montana broke out early on 1 January as people celebrated the New Year.
Seventeen of those killed were aged 16 or under.
Those already under investigation include the bar's French owners - husband and wife Jacques and Jessica Moretti - who face charges of manslaughter by negligence, bodily harm by negligence and arson by negligence.
Jacques Moretti is set to be questioned again by public prosecutors on 5 June.
"We must commend the progress of the investigation and the sustained pace of the hearings. We are making progress, and for the families, this is invaluable," Romain Jordan, a lawyer representing several victims' relatives said.
The announcement follows a second wave of hearings in the case, held over the past few weeks in the Wallis capital Sion.
Among those interviewed was Crans-Montana mayor Nicolas Feraud, who said on Monday he had not been aware that annual safety inspections had not been carried out for six years at Le Constellation.
He insisted that his staff had the necessary resources to do the checks.
Prosecutors believe the fire started when champagne bottles with sparklers attached were raised too close to the ceiling in the bar's basement level, igniting the sound-insulation foam.
The Federal Office for Civil Protection said that as of yesterday, 38 patients were still in hospitals and rehabilitation clinics: 19 in Switzerland and 19 in neighbouring countries.
The Wallis public prosecutor's office said that it had rejected a request by Garen Ucari, a lawyer for one victim's father, for an extraordinary prosecutor to be appointed to oversee the investigation.
"The Crans-Montana tragedy is an extraordinary event with an international dimension and significant media coverage, for which the criminal liability of elected officials and employees of the cantonal or municipal administration may be called into question," it said in a statement.
It said such cases fall under its own jurisdiction and the office had been reinforced with extra staff - and thus considered it had "the means to ensure the efficient handling of the proceedings, in accordance with the principles of independence, objectivity, and expediency."
