Adults who led their family to their deaths in Switzerland planned the event, Swiss investigators say.
The case, which shocked Switzerland, will now be closed.
Police have ruled out any outside intervention, and say the adults, who moved to Switzerland from France two years earlier, gave no sign they were considering suicide.
Four of the family died on 24 March last year in Montreux.
An eight-year-old girl, a 15-year-old boy, their father and mother, and the mother's twin sister fell from their seventh floor apartment.
The boy was in a coma but has now recovered from his serious injuries. He has no memory of that day, investigators say.
Forensic evidence revealed no sign of a struggle before the deaths, and autopsies showed no trace of drugs.
After a year of investigation, the Swiss authorities now say the mother of the family, and her sister, were deeply involved in survivalist and conspiracy theories.
After the deaths, police found their apartment full of food, medicines, and hygiene materials, carefully stored and organised. The family rarely went out, and the children were home-schooled.
The two women had a deep-seated suspicion of government and local authorities, investigators say, and had brought up the children to believe that the world was a hostile place.
The Covid-19 pandemic, and Russia's invasion of Ukraine, had only served to strengthen their conviction.
Searches of the apartment and of electronic devices revealed the collective suicide had been carefully planned, and even rehearsed.
The adults were apparently waiting, the police report says, for the right moment to depart for what they believed would be a better world, away from the one they feared.
Tragically, what appears to have triggered their decision was a welfare visit from Montreux police.
They stopped by that morning to remind the father to go to a meeting with local education authorities to discuss the home-schooling of his son, after he had not answered several letters.
They did not let the police in, and were dead minutes later.
On Tuesday, the Swiss authorities appealed for privacy for the surviving son.