Actually, most people that die in fires don't die from the flames. (directly) they die from the smoke.
so, it's not normally a husk that they find, it's a body, wearing clotes they expect to see, and when they do an autopsy to find the cause of death (they do that first, before identifying it) they find out that it was killed by smoke inhelations...
ID is provided by the surroundings, and the people who knew that he was there.
no reason to pay a couple thousand newyen to run a DNA test when everything points to it being him.
and at best, the DNA test takes two weeks. he'll be replaced by that point, and so far gone that it won't even be worth looking for him.
and, household fires happen all the time. you splash arround a little bit of booze, and put a pack of cigeretes on a nearby counter, and voalla! instant fire-hazard. turn off the smoke detectors (most people who smoke do this anyways) and then you have the reason it got to the lethal stage before the neighbors noticed.
not super easy, but easy enough for out job.
-RuskiFace the Pirate