I expect that there will still be arson investigators in the next decade. I see no reason to think that this is the last decade in human history in which anyone is going to commit an act of arson.
Arson is when you intentionally set fire to any structure or building. So no, it doesn't matter if you did it out of anger or not. If you did it on purpose it's arson.Another View: Arson is defined...
To investigate all leads, all witnesses, and all evidence in the case that is assigned to them in an effort to make an arrest - close the case, and bring the perpetrator to justice.