A defense contractor that supplied interrogators to the notorious Abu Ghraib prison in Iraq argued Friday that it can't be sued for abuses that occurred there because its employees were working in tandem with military personnel whose judgment about conducting wartime operations shouldn't be questioned by a federal judge. Four former inmates at Abu Ghraib sued a subsidiary of Arlington-based CACI International Inc. back in 2008, saying CACI employees conspired to torture them to soften them up for interrogations.