When prosecuting a criminal case, the government may often benefit from an assertion that the investigation was conducted by the book, using the best methods available. But a criminal defendant has an opportunity to present a complete defense and challenge this assertion. This can include an argument that the investigation was not sufficient.

Recently, an appeals court reversed a trial court’s criminal conviction, deciding that the trial court had committed a reversible error by refusing to allow an expert witness to testify on behalf of a criminal defendant. In this case, a man was convicted of various weapons possession charges after the court refused to allow the defendant’s fingerprint expert to testify.

The defendant was charged with a variety of weapons charges, including the unlawful possession of a firearm. The prosecution called on a fingerprint expert to testify. The expert said that a fingerprint found on the gun was unusable. The defense contended that she had not used the proper method of fingerprint recovery and sought to call its own expert witness. The court refused.

The defense sought to call an expert witness to demonstrate, among other things, that the investigation was not of sufficient quality to establish the guilt of the defendant. It may have been that there was a fingerprint on the gun which could have excluded the defendant as a suspect, but that this evidence was never presented because of the inadequate investigation techniques.

The appeals court noted that the case against the defendant was not particularly strong due to an absence of evidence connecting the suspect to the gun. The appeals court reversed the conviction after indicating that the testimony of the expert may have created a reasonable doubt of the suspect’s guilt in the mind of the jurors.

Source: District of Columbia Court of Appeals “MICHAEL SMITH, APPELLANT, v. UNITED STATES, APPELLEE,” Sept. 8, 2011