Case law of Brady v. Maryland, 373 U. S. 83 (1963),  was a United States Supreme Court case in which the prosecution had withheld from the criminal defendant certain evidence. The defendant challenged his conviction, arguing it had been contrary to the Due Process Clause of the Fourteenth Amendment to the United States Constitution. Maryland prosecuted Brady and a companion, Boblit, for murder. Brady admitted being involved in the murder, but claimed Boblit had done the actual killing. The prosecution had withheld a written statement by Boblit confessing that he had committed the act of killing by himself. The Maryland Court of Appeals had affirmed the conviction and remanded the case for a retrial only of the question of punishment. The court held that withholding exculpatory evidence violates due process "where the evidence is material either to guilt or to punishment"; and the court determined that under Maryland state law the withheld evidence could not have exculpated the defendant but was material to the level of punishment he would be given. Hence the Maryland Court of Appeals' ruling was affirmed. Brady refers to the holding of the Brady case, and the numerous state and federal cases that interpret its requirement that the prosecution disclose material exculpatory evidence to the defense. Exculpatory evidence is “material” if “there is a reasonable probability that his conviction or sentence would have been different had these materials been disclosed. ”  Brady evidence includes statements of witnesses or physical evidence that conflicts with the prosecution's witnesses , and evidence that could allow the defense to impeach the credibility of a prosecution witness. Police officers who have been dishonest are sometimes referred to as "Brady cops. " Because of the Brady ruling, prosecutors are required to notify defendants and their attorneys whenever a law enforcement official involved in their case has a sustained record for knowingly lying in an official capacity. Brady evidence also includes evidence material to credibility of a civilian witness, such as evidence of false statements by the witness or evidence that a witness was paid to act as an informant
This article originally appeared in the FBI Law Enforcement Bulletin, December 1992. In March 1990, an unknown assailant sexually molested and fatally stabbed a young woman. At the crime scene, an investigator discovered few leads. The only evidence was a pillowcase, found adjacent to the victim's body, that exhibited several bloodstains. One stain showed some faint fingerprint ridge detail, barely visible even to the trained eye.
An investigator took the pillowcase to the department's forensic unit for bloodstain pattern analysis. Technicians photographed and studied the stains,slowly extracting information. They discovered two things. First, they confirmed that several stains were consistent with blood transfer from a knife blade, although no knife was found at the crime scene. Second, and more importantly, analysts determined that the fingerprint presented enough ridge detail to conduct a more...