Speaking to Geveva daily, Tribune de Genève, the chief prosecutor for the La Côte region in canton Vaud, Jean-Marie Ruede, a farewell note from the father had been found.

In the letter the father, a manager with a pharmaceutical firm in Neuchâtel, indicated “life was no longer possible for him” at least from a professional point of view, the official said.

“He changed firms a year ago and he wasn’t happy there,” Ruede added.

While the authorship of the letter has yet to be formally established, investigators are now working on the theory that the father, who had been on sick leave for some time, had killed his wife and son before taking his own life.

The fact that the father was found in the ground floor of the family home while his wife and son were found upstairs is also possible evidence that this was the case, the prosecutor said.

Maude said he believed the deaths may have been caused by an overdose of medication. Autopsies of the bodies of the woman and her son had revealed no evidence of firearm or knife wounds.

The bodies of the three family members were found on Monday evening after concerned residents contacted police saying they had not heard anything from their neighbours.

The time of death is not yet known, but the La Côte prosecutor said the family had not been seen since last Thursday while the latest social media posts from the family dated back to the same day.