1. If the accounts were his parents', the only way he'd be on a Fed warrant for it is if they were saying they didn't give permission (since they are alive, it's possible to ask and for them to give authority). And some young adult taking money from his live parents ' accounts isn't going to trigger a manhunt involving multiple agencies.
So, obviously not.
2. If his name is not on the account, the money is not legally his without some sort of legal proceeding. If she is dead, she can't authorize anything.
It's one thing to play skeptic; it's another thing entirely simply to be contrary and to ignore known facts + common sense. And basic law, to a degree.
"Reasonable doubt" (which, btw, is not required nor expected at this stage) is not the same thing as alternate reality.