bobbob,

Having once been a Federal Firearms Licensee, I do have a working knowledge of what the ATF is and what it does.  I also happen to know that despite they themselves continuing to use the abbreviation ATF, the full name of the agency is now the Bureau of Alcohol, Tobacco, Firearms and Explosives.

Looking at my earlier comment carefully, you'll note that I left open the question of whether the ATF is summoned if there are multiple deaths from a single fire.  I hate to again burst localguy's bubble, but I know for a fact that a single death, even one where the cause of the fire could not be determined, is not sufficient to have the ATF enter and supplement an investigation.