Police say they are considering every line of inquiry into cause of Geneva blaze.
The virulent campaigning prompted Doris Leuthard, the Swiss economy minister, a Christian Democrat, to warn that it could frighten away foreign investors.
The Free Democrats (FDP) took 15.9 per cent of the vote in the alpine nation, a slight decline from 2003, while the centre-left, family-friendly Christian Democrats were steady at 14.6 per cent.
The Greens took 9.5 per cent of the vote, an increase of 1.8 percentage points.
Voters cast their ballots to fill 200 seats in the National Council, the lower house, on a proportional basis.
They also voted to elect 46 cantonal representatives to the Council of States, the upper house.