McCarthy has been involved with the military commissions at Guantanamo Bay detention camp where over 250 suspected Enemy combatants and terrorists are being held to await trial.

He is chief prosecutor of the Judge Advocate General's Corps of the United States Navy at the Guantanamo Bay Naval Base.

McCarthy is also the one who introduced Ex parte Quirin to Lieutenant Commander Charles Swift which would become bases for the military tribunals at the Guantanamo Bay detention camp.

While Lieutenant Commander Charles Swift was at the base McCarthy was his supervisor and close friend.

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