Agree...likely residue in the room rather than active use.
Cops end up in hospital when dealing with this stuff. Residue can knock you off . So incredibly dangerous.
Except any level of residue that would have affected the sudden death of the woman should have had some effect on the husband.
Pesticide use of chemicals that are illegal in the US and civilized countries. They fumigate the room and the people checked in before it “aired out”.