The good faith exception was established primarily in United States v. Leon in 1984. That case said that the exclusionary rule should not be used to suppress evidence seized in objectively reasonable reliance on a warrant issued by a magistrate, in cases in which the magistrate and not the police made the mistake. Two related cases were Massachusetts v. Sheppard and Illinois v. Krull. The exception applies only in cases where evidence is seized pursuant to a warrant, modifies rather than eliminates the exclusionary rule, and requires that the police officer's reliance on the magistrate's probable cause determination must be objectively reasonable. The good faith exception does not apply if the Fourth Amendment violation relates to improprieties during the implementation of the warrant. In addition, the burden is on the prosecutor to plead and establish the good faith exception. Furthermore, whenever suppression of the evidence under the particular circumstances should arguably deter the police, the good faith exception should not apply. The four exceptions to the good faith exception involve the lying police officer, the prosecutorial magistrate, situations that clearly lack probable cause, and warrants that are facially deficient. When considering a warrant, attorneys must also consider issues such as training of the police, judge shopping, prosecutorial advice, whether illegal warrantless activities occurred prior to applying for the warrant, flagrant misconduct on the part of the police, and cost- benefit analysis. Summaries of specific judicial decisions