Evidence obtained illegally is generally inadmissible in criminal cases due to the exclusionary rule, which is rooted in the fourth amendment of the U.S. constitution and reinforced by california’s constitution. This rule is designed to prevent evidence obtained through unconstitutional means, such as illegal searches or seizures, from being used against a defendant in court. The exclusionary rule was established at the federal level in mapp v. ohio (1961) and adopted by california courts in people v. cahan (1955). Additionally, the fruit of the poisonous tree doctrine further prohibits evidence derived from illegally obtained materials from being admitted, unless an exception applies.

There several exceptions to the exclusionary rule. The good faith exception allows evidence to be admitted if law enforcement officer acted under reasonable belief that their actions were legal, such as relying on a defective warrant. The independent source doctrine permits evidence to be used if it was obtained through lawful means independent of the illegal conduct. Similarly, the inevitable discovery doctrine allows the admission of evidence if it would have been found through lawful procedures regardless of the initial constitutional violation.

Defendants can challenge illegally obtained evidence by filing a motion to suppress under california penal code §1538.5. If granted, the suppressed evidence cannot be used at trial. The burden of proof typically falls on the defense to show that the evidence was obtained unlawfully, while the prosecution may argue that an exception applies or that the search was legally justified. While illegally obtained evidence is generally inadmissible in criminal proceedings, it may still be used in some non-criminal cases, such as civil or administrative hearings. The exclusionary rule ultimately serves to deter unlawful law enforcement practices and protect the constitutional right of individuals facing criminal prosecution.