An obscure law approved by a Republican-controlled Congress a decade ago has made the Bush administration nervous that officials and troops involved in handling detainee matters might be accused of committing war crimes, and prosecuted at some point in U.S. courts.
Senior officials have responded by drafting legislation that would grant U.S. personnel involved in the terrorism fight new protections against prosecution for past violations of the War Crimes Act of 1996. That law criminalizes violations of the Geneva Conventions governing conduct in war and threatens the death penalty if U.S.-held detainees die in custody from abusive treatment.
You can’t change the law after the fact; only the law that was in place at the time the crime was committed, counts. This is similar to Specter’s attempt to legalize the wiretapping crimes retroactively. It’s illegal.