I cannot offer any legal advice, but my experience in similar cases is never to underestimate the greed of humanity, whne some 'money for nothing' is on offer. Nor should you trust anyone who might have claim, or think they have claim, for the money to act helpfully toward you. Never mind who is 'morally' right, they just want to money.
The verbal 'las Will & Testament' has no legal standing if it was not witnessed. nor vry little even if there was a witness. Remember that said friend could easily have made the whole thing up simply to cover his theft of the bank cards and other stuff. Why else would he have taken that and not be wanting to return it to the correct owner.
Try to keep written records of every communication you have with friend, and keep detailed notes of everything, every phone call, visit to bank, just about everything. if it come down to "I said, he said" you will need every scrap of evidence.