Charles Graner was released from prison on Saturday

A U.S. military guard known as a ringleader in the physical abuse and sexual humiliation of detainees at Abu Ghraib prison was released Saturday after serving more than six years in a Kansas military prison barracks, a U.S. Army spokesperson said.

Charles Graner, 42, was released from the U.S. Disciplinary Barracks at Fort Leavenworth, Kansas, after serving six-and-a-half years of his 10 year sentence, said U.S. Army spokeswoman Rebecca Steed.

Graner, a former U.S. Army reservist was credited with good conduct. He served his prison term as a private, with no salary and was to be dishonorably discharged after the release.

Graner, along with six other members of the 372nd Military Police Company, were charged in January 2005 for allowing and inflicting sexual, physical, and psychological abuse of Iraqi prisoners of war in Abu Ghraib Prison, a notorious prison in Baghdad during the United States' invasion of Iraq. Graner was convicted on charges of conspiracy to maltreat detainees, failing to protect detainees from abuse, cruelty, and maltreatment, as well as charges of assault, indecency, and dereliction of duty.

The images of the abuse were first revealed in a military inquiry report. It received public attention after a "60 Minutes II" news report and an article by Seymour M. Hersh in "The New Yorker" magazine in 2004.

A picture obtained by ABC News and released May 19, 2004 shows Charles Graner posing over the body of detainee Manadel a-Jamadi who died from torture in Abu Ghraib prison.

The horrific photographs show some guards abusing and humiliating the detainees and displaying obvious satisfaction at the acts.

Images showed Graner giving the thumbs up sign behind naked Iraqi prisoners piled up in a heap. Another picture shows him giving the thumbs up over a corpse of an Iraqi prisoner, who died from excruciating torture. He is also seen punching or pretending to punch a group of handcuffed prisoners. One prisoner told military investigators that Graner forced him to stand on a food box, naked except for a blanket. Another soldier then put a bag over his head and electrodes on his fingers, toes and penis. This incident's picture appeared on The Economist's cover and was one of the first pictures that prompted the investigation.

The maltreatment of detainee charges accused Graner, among other things, of ordering prisoners to masturbate in front of other detainees and soldiers and simulate a sex act; and encouraging former Private First Class Lynndie England to drag a prisoner by the leash.

England, Graner's ex-fiance, was also sentenced to three years in prison.

All in all, 11 military personnel were convicted for prisoner abuses at Abu Ghraib. Graner will be under supervision by a probation officer until Dec. 25, 2014, Steed said. Hana Adwar, an Iraqi human rights activist, told The Associated Press news agency that his release would be met with outrage in Iraq.