Swiss police believe that four French family members committed suicide by jumping from their apartment balcony.
Three adults and an eight-year-old girl died last week after falling more than 20 metres from their flat in the lakeside city of Montreux.
A 15-year-old boy was also left seriously injured and remains in a coma in a stable condition in hospital.
Police in Vaud said in a statement on Tuesday that they ruled out any third party involvement in their deaths.
"The investigation into the tragedy that occurred in Montreux ... suggests that all the victims jumped from the balcony one after the other," police said.
"The police discovered a stepladder on the balcony and no evidence of a struggle."
Police were initially called to the property to execute a warrant in connection with the home-schooling of a child.
Officers then left could not contact the occupants, before a witness reported that people had fallen from the apartment balcony.
"After five days of investigation ... the prosecutor and the cantonal police investigators are favouring the possibility of collective suicide," police said.
Authorities also say that the family had tried to seclude themselves from authorities in Montreux.
"Since the beginning of the pandemic, the family had been very interested in conspiracy and survivalist theories," the statement read.
"They had built up an impressive stockpile of all kinds of foodstuffs, very well organised, occupying most of the different rooms in the flat, to enable them to cope with a major crisis.
"The family lived in virtual autarky, withdrawn from society. Only the mother's twin sister worked outside the home."
Police also said that the mother and 8-year-old girl had not been registered with local authorities and had last been recorded leaving Morocco in April 2016.
"The family lived in seclusion and must have feared that the authorities would interfere with their way of life," police added.
All the victims were formally identified as members of the same family of French nationals -- the 40-year-old father, his 41-year-old wife, her twin sister and the couple's 8-year-old daughter.