For a class case analysis, this has a number of points we need to discuss when it comes back on line somewhere. Disgruntled workers, if as reported this is, can always be a threat, but there is not a single point of analysis that you can point to and say this one is going bad. But if you study the issue, there are points to look at that may let you paint a risk analysis showing a higher threat. One of the first is they state they are unhappy about something. It is like when I take students thru the points of a bomb threat, actually any threat. Normally there is no one statement or action that tips the scale to believe the threat, it is a number of things, that bring you to that conclusion. It is the same here, there may have been a number of points if analysed together may have pointed to the actions taken by this individual. If you are a fellow employee, tell management your concerns, if your are management, take in all the management, and if you need help in doing the risk analysis get hold of a reputable security consultant, or if you do not know one, call the Police. Most of the time the Police, have either little they can do, or they have a duty to react, that indeed be an over reaction, that they can not control. But right now every business out there should be reviewing how they handle disgruntled employee's. Dust off your plan and make sure it is workable.
from CTI Consulting https://www.youtube.com/watch?v=cl8okt4BuU4