In the case of Illinois v. Krull et al., 1986, the U.S. Supreme Court ruled that evidence obtained by police officers acting in good faith reliance on a statute later found to be unconstitutional could be used in court proceedings. The case involved an Illinois law allowing warrantless searches of auto junkyards and vehicle dismantlers, which was subsequently declared unconstitutional for violating Fourth Amendment protections against unreasonable searches and seizures. However, during the period when this law was still considered valid, police had searched Michael Lee Krull's auto wrecking business without a warrant and discovered stolen vehicles parts leading to his prosecution. In its decision (6-3), the Supreme Court extended 'good-faith exception' doctrine from previous cases involving flawed search warrants to situations where officers were following statutes they believed at that time were constitutional.

In the dissenting opinion for Illinois v. Krull, it was argued that the majority's decision to allow evidence obtained in violation of the Fourth Amendment due to a police officer's reliance on an unconstitutional statute undermined constitutional rights and protections. The dissent emphasized that this ruling could potentially encourage lawmakers to pass more unconstitutional laws with knowledge that any evidence collected under them would still be admissible until they were struck down by courts. They also pointed out inconsistencies in how good faith exceptions are applied, arguing that if ignorance of law is not excusable for citizens then it should not be so for law enforcement either. Furthermore, they contended there was no compelling reason or urgency justifying such erosion of Fourth Amendment protections since other legal remedies like civil suits against states passing unlawful statutes already existed.