I have the name and date of death of a US Service Member that I believe died in the early days of the Vietnam Conflict. However, I cannot verify if he died in Congo, Panama, or some other theater instead. The date on his grave marker is September 27, 1964.
How do I go about getting his Military records and an explanation of his death?
Contact the National Archives, specifically the archive at College Park, Maryland. They have the US Army records for all post-war soldiers, and should be able to help you in your research. And even if they dont have what you want (though they really should), and archivist there can at least point you in the right direction. You should shoot them an email.