The convicted ringleader of detainee abuses at Abu Ghraib has been released from a US military prison

The convicted ringleader of detainee abuses at Abu Ghraib has been released from a US military prison, an army spokeswoman said.

Charles Graner Jr was released on Saturday from the US Disciplinary Barracks at Fort Leavenworth, Kansas, after serving more than six and a half years of a 10-year sentence, spokeswoman Rebecca Steed said. Graner, 42, will be under the supervision of a probation officer until December 25, 2014, she said.

Steed said she could not release any information about Graner's whereabouts or his destination after release. Graner's wife was a fellow Abu Ghraib defendant.

Graner was an Army Reserve corporal when he and six other members of the Maryland-based 372nd Military Police Company were charged in 2004 with abusing detainees at the prison in Iraq.

The strongest evidence was photographs of grinning US soldiers posing beside naked detainees stacked in a pyramid or held on a leash.

The pictures complicated international relations for the US and provoked debate about whether harsh interrogation techniques approved by the Pentagon amounted to torture.

Graner is the last Abu Ghraib defendant to be released from prison and received the longest sentence.