kinda...
While it is odd that it went all the way to an attorney, basically everythign is standard. Anytime a person makes a comment such as this, which may or may not be construed as a threat to a government official, it must be investigated. Many times it is dismissed as not a true threat, perhaps even something off the cuff or intended for humor, but not always.
This was something that was convered in training regarding client confidentiality when I worked in mental health. I never realized that this went back to when Nixon was in office...I wonder when this became the standard practice.