In a decision released today, Smith v. Cain, No. 10-8145 (S. Ct. Jan. 10, 2012), the United States Supreme Court overturned a Louisiana conviction of Juan Smith because the State did not turn over exculpatory evidence that contradicted the testimony of an eyewitness who testified at trial. Failing to turn over material evidence is a violation of the landmark Supreme Court case of Brady v. Maryland.
In the case, the Court concluded that notes in a police detective's file showing that the sole eyewitness who placed Smith at the scene of the crime were exculpatory and were material to the determination of the defendant's guilt. The missing files showed that the lone witness had told a police detective he "could not ID anyone because he couldn't see faces", that he "would not know them if he saw them," and that the witness "could not identify any of the perpetrators of the murder."
Prior Supreme Court cases, such as Untied States v. Agurs, 427 U.S. 97 (1976) have held that evidence impeaching an eyewitness may not amount to a Brady violation "if the State's other evidence is strong enough to sustain confidence in the [guilty] verdict." In Smith v. Cain, however, the only evidence linking Smith to the crime was the testimony of a single eyewitness. The undisclosed evidence that would have impeached this testimony was material.