My grandfather in Russia recently died, and he was very private about the state of his finances and did not leave a will. Because of that, nobody, not even his son, really knows what he's worth. He owns three properties and was the head of a business, and it's unclear what he had in terms of bank accounts. Is there a specific person who can be hired to do the research on his affairs at death to determine what exactly the value of his estate is?
Generally, it would be an accountant. Specifically in the case of very "private" (or unorganized, which is even worse) person - forensic accountant.
Since there's no will - it will probably require a lawyer as well to gain access to all the accounts the accountant discovers.
I would start with a good estate attorney, who in turn will hire a forensic accountant to trace the accounts.