Steve,
It's not all that complicated. If the burglar or vagrant intended to set the structure on fire it's incendiary. If the person did not intend the building to burn down, it's acidental. If you don't know, you don't know - its undetermined.
The fact that the investigator is understandably reluctant to say undetermined has nothing to do with it. If the investigator is unwilling, or afraid to buck the supervisors or his/her peers, then the investigator should seek employment elsewhere.
As long as we are talking about posterboys - you are in fact the preminent posterboy for refusing to give into such pressure in the face of truth. That is why I and many others applaud you!
Pat Kennedy, CFEI, CFPS, MIFireE
Fire and Explosion Analyst
Sarasota, Florida
[
www.kennedy-fire.com]