Bomb threat

Yesterday morning a bomb threat claimed the Tokyo Stock Exchange, Nomura Securities, and Tokyo Station would be blown up. They're still standing today; apparently it was a hoax. But here's an interesting point:

800 people were evacuated from the TSE while the police spent 30 minutes looking for bombs. Nomura's office building and the train station were not evacuated or disrupted in any way (though one must assume the police did check for bombs there). Why evacuate one and not the other two?