SAN JUAN, Puerto Rico – An Afghan man who is being held with the most significant terrorism suspects in U.S. custody has apparently gained extensive knowledge of western pop culture in an unlikely place: the top secret prison-within-a-prison in Guantanamo Bay.

Nearly five years ago, Mohammed Rahim al-Afghani became the last prisoner sent to Guantanamo. He was accused of helping Osama bin Laden elude capture, and the CIA had interrogated him for months at an undisclosed location before he was locked away in Guantanamo's Camp 7, a prison unit shrouded in secrecy that holds about 15 men who have been designated "high value" detainees by the U.S. government.

With no court appearances, or even charges filed, nothing was heard from Rahim and he has remained largely a mystery. So, it was a surprise when his lawyer, Carlos Warner, released letters from the detainee described by the head of the CIA as a "tough, seasoned jihadist." More surprising still was the content: quirky notes peppered with references to Howard Stern, Fox News and the global video hit of South Korean singer PSY.