Yesterday I went by bus from the Euroairport (French sector) to Zurich. Unusually, two Swiss border checks took place.
First, at the St-Louis border checkpoint, officials boarded the bus, asking foreigners (including me) where they were going, for what purpose and for how long, and collecting all passports for scanning. This check took 30 minutes.
10 minutes after leaving the border, the bus stopped at the scheduled bus stop in Basel, where a mobile team of officials boarded with portable passport devices. They scanned all passports and visas and checked entry/exit stamps. Myself I was asked where I was going, where in Switzerland I live, for what purpose I live there, where I was travelling from and for how long I'd been there. This check took 15 minutes.
How come the same authority (the Grenzwache) would check the same bus twice, given that no passengers can get on/off the bus between the border and the bus stop in Basel?