I can’t open the linked article, probably for reasons related to the data protection regulation that applies in the EU, so not knowing the details of this particular case I will just say that it surprises me that this method of political/social disruption is not used more often. When the first anthrax scares by mail were reported around the time of 9/11 it was widely reported, buildings were evacuated and so on, all for the price of a stamp. I hope this Kansas case does not trigger a wave of copycat events. I also wonder how the police and the security services will try to get the perpetrators: if they are careful it should be hard.
Does the article mention whether the white powder is dangerous or just sugar? I believe back in 2001 at least some of the letters were anthrax spores, which is not easy to obtain and really dangerous. I also recall that the attacks stopped without a culprit being found.