Your immediate contact depends of where the death occurred. Read the scenarios below, however in all scenarios it cannot be stressed enough to contact EUSA Casualty Assistance Office (CAO) as soon as possible.
Notify the U.S. Embassy in Seoul Korea by calling their 24-hour switchboard at +82 (0)2 397-4114 and request a Consular Reports of the Death of a U.S. Citizen Abroad (CRODA).
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If your deceased retiree spouse has created a Family Protection Plan, pull it out and begin reading through it. It should list accounts, points of contacts, and information you will need to contact and work with banks, credit card companies, insurance agents etc.
For more detailed information, check out theses links: