He sent his letters mainly to newspapers and television stations, but some Starbucks have also reported receiving letters. Keyser didn't keep his letters local, his letters have gone as far as Boston, where two newspaper offices had to evacuate their buildings. Offices in Minneapolis have also received these envelopes.
I watched a report on this man earlier today on the news, they said that he has been arrested for the same crime before, but was let go because no real harm was caused. They are not sure if he will be let go for a repeat offense, especially when the effects were so far reaching this time.
Personally I don't know why Keyser would do something like this, especially twice. There seems to be no real connection between the places he sends his letters other than they are mostly news buildings, nor a reason for him to be sending anthrax threats to these places. I think it has to be something more than just a prank, because if he was arrested already for doing this why would he risk it again? Also, a lot of work went in to addressing the envelopes as well as placing things in them, more work than I think would be done for some prank.
It probably won't be long before investigators find a reason for Keyser's actions, and when asked if he would do it again he was quoted as saying "Absolutely"
From The Boston Channel