In U.S. criminal courts, juries typically get instructions before beginning deliberations something like this model jury instruction:
The fact that a witness is employed as a law enforcement officer does not mean that (his)(her) testimony necessarily deserves more or less consideration or greater or lesser weight than that of any other witness.
But recently the U.S. Court of Appeals for the D.C. Circuit agreed with the arguments of the Obama administration and decided in the case of a Guantanamo detainee (
LATIF v. Obama, Court of Appeals, Dist of Columbia Circuit, 2011) that a detainee can only win a habeas petition if he "has rebutted the Government's evidence with more convincing evidence of his own."
The Obama administration, in arguing for this outcome, is playing a role straight out of "The Trial" or "Darkness at Noon". Please see "Losing Interest", a commentary by Erwin Chemerinsky in The National Law Journal for a better discussion of this travesty.