They will have been smoking though won't they- I mean if they're up on the roof they're not going to go all the way down and away from the building to have a smoke and then come all the way back up are they? They'll have been up there with their packed lunch of jambon berre and a glass of vin...
Police are interviewing the contractors- my first question would be - 'Right lads- who smokes?' Any answers of 'Moi' / 'Oui' and you've got your list of prime suspects!