Giving video testimony at Graner's court martial on Tuesday, Ameed al-Shaikh said Graner beat him mercilessly while he was recovering from a bullet wound and laughed as he writhed in pain.
"He was the primary torturer," said al-Shaikh, a Syrian national
"That Graner guy is a man who hurt his country, hurt his people and I think he will receive his punishment," he added.
He said Graner forced him to eat pork and drink alcohol - practices against his Islamic religion.
Another former inmate described how he was sexually humiliated.
"They were torturing us as though it was theatre for them," said Husayn Mutar. "I couldn't believe in the beginning that this could happen, but I wished I could kill myself because no one was there to stop it."
Graner and Private Lynndie England, with whom he fathered a child and who is also facing a court martial, became the faces of the Abu Ghraib prison scandal after they appeared smiling in photographs that showed degraded, naked prisoners.
The pictures further eroded the credibility of the United States, already damaged in many countries by the Iraq invasion.
The abuse pictures shocked the
world and shamed the US
At the trial, military prosecutors have presented evidence not seen before in public from Abu Ghraib, including a video of forced group masturbation and a picture of a woman prisoner ordered to show her breasts.
Graner's lawyer, Guy Womack, however, insists his client was only following orders to soften up prisoners for military intelligence agents.
He also said activities such as making human pyramids with naked hooded prisoners were acceptable.
Womack also justified England holding a crawling naked Iraqi man on the leash, saying using a tether was a valid method of controlling detainees, especially those who might be soiled with faeces.
"You are keeping control of them. A tether is a valid control to be used in corrections," he said. "In Texas, we'd lasso them and drag them out of there."
If proven guilty, Graner could be handed a 17-year prison sentence.
Since the scandal broke last year, the Bush administration has blamed a small group of soldiers.
But investigations have shown many prisoners in Iraq, Afghanistan and at the US navy base at Guantanamo Bay in Cuba also suffered abusive treatment after the government considered improving its method of obtaining information in its "war against terror".