For evidence to be admissible in a criminal prosecution it generally must have been obtained legally—with a search warrant, or based on an exception to the search warrant requirement, such as consent to search—and be relevant and reliable.
In Maryland, as in other states, evidence must be obtained legally to be admissible in a criminal prosecution. This means that law enforcement officers typically need to obtain a search warrant before conducting a search that would otherwise violate an individual's reasonable expectation of privacy. However, there are several exceptions to the search warrant requirement, such as when an individual gives consent to a search, when evidence is in plain view, during exigent circumstances, or when the search is incident to a lawful arrest. Additionally, the evidence must be both relevant to the case and reliable to be admissible. Maryland courts will exclude evidence that was obtained in violation of the Fourth Amendment, which protects against unreasonable searches and seizures. This is in line with the exclusionary rule, which is a legal principle that prevents evidence collected or analyzed in violation of the defendant's constitutional rights from being used in a court of law. The reliability of evidence is also scrutinized, and factors such as the chain of custody and the integrity of the evidence collection process are considered.