Final answer:
In Mapp v. Ohio (1961), the Supreme Court ruled that illegally seized evidence may not be used to obtain a conviction, thus establishing the exclusionary rule at the state level. This principle is referred to as "fruit of the poisonous tree," which also applies to secondary evidence derived from an illegal search or seizure.
Step-by-step explanation:
Mapp v. Ohio (1961) Supreme Court Ruling
In the case of Mapp v. Ohio (1961), the Supreme Court ruled that evidence seized illegally may not be used to obtain a conviction. This established the exclusionary rule at the state level, thereby incorporating it into state courts as well as the federal level. Prior to this case, the exclusionary rule had been applied in federal courts following the Weeks v. United States decision in 1914. The Mapp decision was significant for extending this protection of Fourth Amendment rights against unreasonable searches and seizures to state courts, emphasizing that illegally obtained evidence, as well as any evidence derived from such illegal activity, cannot be admitted as it is known as "fruit of the poisonous tree."
However, there are exceptions to the exclusionary rule, such as the "good faith" exception and the "inevitable discovery" exception, where evidence may be admitted even if there was an error in the legal procedure as long as certain conditions are met. Nonetheless, the core principle established by Mapp v. Ohio restricts the use of evidence gathered through illegal means.