In the 1967 case of Harrison v. United States, the Supreme Court ruled that a defendant's testimony given at a previous trial could not be used against him in a subsequent trial if it was elicited by illegally obtained evidence. The court held that such use would violate the Fifth Amendment's protection against self-incrimination. In this case, three confessions were made by Harrison and later deemed to have been coerced, thus making them inadmissible as evidence. However, when he testified on his own behalf during his first trial (which resulted from these confessions), he essentially repeated what he had said in those initial statements. When retried for murder after an appeal due to unrelated issues with jury instructions, prosecutors introduced into evidence portions of his earlier testimony since they no longer had access to the original confessions which were now excluded as evidence because they were unlawfully obtained.

In the dissenting opinion for Harrison v. United States, Justice Harlan disagreed with the majority's interpretation of the "fruit of the poisonous tree" doctrine. He argued that there was no direct causal connection between Harrison's illegal arrest and his subsequent decision to testify at trial, which led to his conviction. According to Justice Harlan, this lack of a clear link meant that Harrison's testimony should not be considered tainted evidence obtained as a result of an unlawful act (the "poisonous tree"). Instead, he believed it was more likely that Harrison chose to testify due to other factors such as strategic considerations or advice from counsel. Therefore, in Justice Harlan’s view, excluding his testimony would unnecessarily expand the scope of exclusionary rules beyond their intended purpose - deterring police misconduct.