Since this is still a developing story don't you think your mouth is ahead of your brain? I wouldn't expect anthrax to be found in an apartment. Would you considering that anthrax requires a lab to be produced? The next obvious step would be to prepare the letters with anthrax right there in the lab with all the equipment.
It requires a lab to be produced, but not to be stored. Not spores. The anthrax could have been produced somewhere else.