Daniel Knech of the Swiss safety investigation service SESE said the crew did not have time to send out a distress signal.
Police spokeswoman Anita Senti told reporters that it was with "sad certainty" that "the 20 people aboard perished".
Authorities have provided few details about those on board JU-Air's plane which crashed on the west side of the Piz Segnas mountain in the canton of Graubuenden on August 4.
The parents and two children crashed roughly 30 minutes after their plane took off from an airfield in Kägiswil, headed towards France, Swiss police said.
Zimbabwean leader appeals for calm after election violence
Both the opposition and Western election observers have urged that presidential election results be released as soon as possible. Officers responded with tear gas, water cannon and rubber bullets. "I was making a peaceful protest". "This is our government".
Among those killed were 17 people from Switzerland and a three-person family from Austria.
The vintage aircraft crashed into the Piz Segnas mountain in the Flims resort on Saturday.
The area around the crash site, which is popular with hikers and skiers and includes a glacier, was closed to the public.
He said that officials expect the investigation of the cause to be "relatively complex".
Turkish Lira skids past 5 to the dollar on United States sanctions news
Anticipation of the US sanctions had already helped to send the Turkish lira to an all-time low against the dollar on Wednesday. Brunson was held for almost two years in prison on terror-related charges before he was moved last week to house arrest.
JU-Air says it runs a small fleet of four Junker planes, all built in 1939, which are for hire.
The cause of crash is now being investigated by the Federal Prosecutor's Office, in partnership with local Swiss authorities. Knecht said that while heat can affect an aircraft's performance, experienced pilots could deal with that. The JU-Air airline operated three of the vintage planes - decommissioned by the Swiss Air Force and affectionately known as "Auntie Ju" planes - as part of sightseeing tours, Reuters reported.
"We can not yet explain what led to the tragic accident on Piz Segnas", he said.
A brochure on the company's website listed the cost of the 2-day Locarno trip as 1,130 francs ($1,136), including meals and a night in a hotel.
Prince Harry and Meghan have the most elegant joint monogram
The gorgeous piece, which is made out of vegan leather, will be the flawless addition to Meghan's growing roster of bags.
The company did not offer any further information.