Claim alone would fail, yes. But really if this was a regular and customary thing, and there was no evidence that you knew someone was deceased, not sure what penalty would be.Flimsy argument that will fail. Other criminals are caught all the time on surveillance cameras at ATM's using their victims cards. Claiming that they gave you permission doesn't fly.
My cousin mistakenly used her mother’s account shortly after she died. Certainly no warrant for her arrest for that but she did get a stern warning that it was a serious breach. She just didn’t know.
At this point , that BL is a POI, not accused of murder, makes it so that his status would legally speaking like that of someone legitimately driving GP’s van home, say, at her request and permission, and she died unknown to him after he leaves.
I guess the use of her van , registered solely to her does not fall under such federal rules.