A long-term employee, who was among the dead, opened fire with a pistol at the chipboard plant near Lucerne on Wednesday. Police said the 42-year-old man draw his gun without warning and began firing.
Kronoswiss was reported to have announced cutbacks in production due to problems with raw material supply, but Kronospan chief executive Mauro Capozzo said no jobs had been lost and no-one had been laid off recently.
Colleagues of the gunman told news organisations that he had changed over the past year and had been suffering from apparent psychological problems. He talked to himself or people that were not there, one employee said.
Mr Capozzo said at a press conference that the man had been with the company for 10 years, was quiet and that no other incidents involving him were known.
Police, who did not identify the gunman, said the motive was still under investigation.
Kronospan expressed its "shock and grief", which it said was "not possible to put into words".
The shootings occurred during the morning snack break in the workshop, the canteen and the connecting passageway between the two areas.
Switzerland has one of the highest rates of gun ownership in the world. About one in four people own a gun yet crimes relating to firearms are very low.
