You need a lawyer in Greece.
I am a former federal and State prosecutor and now handle criminal defense and personal injury/civil rights cases. Feel free to check out my web site and contact me at (212) 577-9797 or via email at Eric@RothsteinLawNY.com. I was named to the Super Lawyers list as one of the top attorneys in New York for 2012. No more than 5 percent of the lawyers in the state are selected by Super Lawyers. The above answer is for informational purposes only and not meant as legal advice.
Reach out to any relatives in Greece to help locate an attorney there. Also, there is a large Greek community located in the Astoria area, maybe someone there or an attorney there can help you locate an attorney in Greece.
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Have you tried to follow up with your mother's relatives in Greece to see if they can give you any more information about the bank where the funds might be located. You might also check with the Greek government to see if they have any records relating to the event.
Other than that you would definitely need an attorney in Greece to help you; even if you knew precisely where the money is you would most likely need a Greek attorney to help you gain control of it.
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