WASHINGTON (AP) — A basic contradiction lies at the root of an exam-cheating scandal that decimated the ranks of an Air Force nuclear missile group, investigators say: Commanders were demanding perfection in testing and ethics but also tacitly condoned rule-bending or even willfully ignored cheating.

An Air Force investigation concluded that no commanders participated in or knew about the specific forms of cheating in which 91 missile officers were implicated at Malmstrom Air Force Base, Mont. But nine commanders, representing nearly the entire operational chain of command in the 341st Missile Wing, were fired and the wing commander, Col. Robert Stanley, was allowed to resign.