French citizen Ahmed Hadjarab has filed a criminal complaint with his government over his nephew Nabil's continuing imprisonment and torture in Guantanamo Bay.
It states that Nabil Hadjarab's indefinite detention and ongoing torture violates the French criminal code and the Geneva Convention.
Nabil, a client of legal action charity Reprieve, has been imprisoned by the US in Guantanamo Bay since 2002.
He has never been charged or tried, was cleared for release in 2007 and was told by his interrogators that he had been confused with another man and that his detention was a mistake.
Despite all this he is still being held in Guantanamo.
Reprieve spokeswoman Polly Rossdale said: "Nabil has now been held beyond the rule of law for more than 10 years.
"For almost half of this time he has been cleared for release.
"It is now up to the French government to do what is right and seek his release."
Attacks such as yesterday's horrific murder in Woolwich didn't happen before the 'war on terror.' It's time we recognised the consequences of the conflicts we've unleashed