What legal principle holds that illegally obtained evidence cannot be used in court?

The principle that prohibits the use of unlawfully acquired evidence in a court of law is a cornerstone of the American justice system. This legal doctrine ensures that law enforcement adheres to constitutional standards when gathering information for criminal prosecutions. Its primary purpose is to deter police misconduct by removing the incentive to disregard a suspect's rights, effectively preventing the government from benefiting from its own illegal actions.

Rooted primarily in the Fourth Amendment's protection against unreasonable searches and seizures, this rule also extends to violations of the Fifth Amendment's right against self-incrimination and the Sixth Amendment's right to counsel. A critical aspect of this doctrine is the "fruit of the poisonous tree" concept, which dictates that not only is illegally obtained evidence inadmissible, but any further evidence discovered as a direct result of that initial illegal act is also excluded from trial. This ensures that the taint of the original constitutional violation does not spread to subsequent discoveries.

The application of this rule has evolved significantly over time. It was first established at the federal level in the 1914 Supreme Court case *Weeks v. United States*. However, it was not until the landmark 1961 decision in *Mapp v. Ohio* that the Supreme Court extended this crucial protection to state courts, making it universally applicable across the United States. This decision was a pivotal moment, significantly strengthening individual civil liberties and ensuring a more uniform standard of due process nationwide.