Beyond the strict legalities lies the broader questions of policy: Is it the proper role of law enforcement to conduct criminal “morality tests” to determine whether citizens will lie when given the opportunity by FBI agents? I believe the answer should be “No.” The function of law enforcement is to uncover past crimes, not to provide citizens the opportunity to commit new crimes by testing their veracity.
There may be extraordinary situations, such as prevention of mass-casualty terrorism, that justifies the use of highly questionable tactics but, absent such extraordinary circumstances, FBI agents and prosecutors should not deliberately provide citizens the opportunity to commit federal crimes in order to prosecute them, make political points or turn them into government witnesses.
When questioning suspects, officials should not ask questions whose answers they already know, for the sole purpose of seeing whether the suspect will lie. If they do ask such questions, untruthful answers should not be deemed “material” to the investigation, because the FBI already knew the truth. That is the civil liberties approach to proper law enforcement.