Police said Sunday they have now determined that all 20 people on board the plane, including its three crew members, died.
The wreckage of the plane was in a basin at 2,450 metres (8,000 feet) above sea level surrounded on three sides by peaks, a Reuters witness said.
Officials said Sunday they weren't aware of any distress call made from the plane, adding that the investigation into the crash is expected to be "relatively complex" - though there's no indication of foul play. Most were from Switzerland but also a couple and their son from Austria.
It was the first time the airline had experienced an accident that resulted in death or injury to passengers or crew members, Waldmeier said.
The vintage aircraft crashed into the Piz Segnas mountain in the Flims resort on Saturday.
There are now no details on casualties but the Ju-52 can carry up to 17 passengers, two passengers and a flght attendant.
The mountainous area in southeastern Switzerland is popular with hikers and skiers and includes a glacier.
Swiss media have been citing plane experts' speculations that the current heat wave may have contributed to the crashes.
The German-built Junker JU52 HB-HOT aircraft, dating from 1939 and nickamed "Iron Annie", was a collectors' aircraft.
The company's flight operations were suspended, it said.
Chief executive and co-founder Kurt Waldmeier said the planes "are flown exclusively by very experienced professional pilots, and strictly checked and maintained by our own technicians". He said it had its full annual service during the winter, and "we know of no technical problems with this aircraft".
"We can not yet explain what led to the tragic accident on Piz Segnas", he said.
The company did not offer any further information.