He is appealing his case, claiming in part that the instructions given to the jury were flawed because they essentially said he "should have concluded" that his chief financial officer was "perpetuating a massive fraud."

The deliberate ignorance standard is more common in so-called street crimes like drug cases where a package is placed in a car and the driver delivers the package to a customer but avoids discovering that drugs are inside. Mr. Petrocelli likened the Enron instruction to someone knowing someone else is about to jump out a window, closing his eyes and only opening them after the other person has already jumped.

Legal scholars said the use of the instruction is particularly troubling in the Enron case because the government argued a different theory of the case. In an apparent effort to simplify what was long assumed would be a case about arcane accounting fraud, prosecutors argued that Mr. Lay and Mr. Skilling deliberately chose to lie and mislead investors and employees in public statements to keep the fiction of Enron's success going and enrich themselves.

The government, in the end, has not argued that both men shielded themselves from the truth and avoided knowing of illegal acts committed by subordinates.

"The government hasn't presented that sort of approach," said Ellen S. Podgor, a law professor specializing in white-collar crime at Stetson University. "They have presented a case where this was a guy on the soapbox telling the public lies."

Mr. Androphy, who has been following the case closely, agreed. "The government can't argue a theory, offer evidence on a theory and then do a 180 and argue for an instruction on an alternate theory," he said. "That's not permissible."

Judge Lake allowed the instruction after the government opposed a defense motion to keep it out. The government said in a filing with the court last week that both Mr. Lay and Mr. Skilling asserted the "ostrich defense" by claiming they knew of no wrongdoing other than the crimes committed by the chief financial officer, Andrew S. Fastow.