Saw someone mention the common theme of numerous mass shooters stating their episodes of destruction were preceded by an onset of voices in their heads. Here is a specific patent titled "Method and Device for Implementing the Radio Frequency Hearing Effect". It talks about a means of voice transmission through the skull using microwave radiation.
Patent # 6470214 Dated Oct 22 2002
This is in conjunction with a man named Dr Robert Duncan.
This material is the subject of a 2012 (?) Episode of Conspiracy Theory with Jesse Ventura S03E06