Smith v. United States, 27 A.3d 1189

Michael Smith was convicted of carrying a pistol without a license, unlawful possession of a firearm, and related offenses in the DC Court of Appeals.
The defense sought to admit fingerprint expert Wynn to rebut government witnesses on fingerprint recovery methods and police investigation quality.
The trial court excluded Wynn's testimony on relevancy grounds, relying on Jackson v. United States to deem it irrelevant.
The government argued Wynn's testimony would be cumulative and confuse the jury, and that cross-examination adequately exposed any issues.
The DC appellate court held the exclusion of Wynn's testimony was an abuse of discretion and reversible error, given the defense theory and case strength.
The court remanded for a new trial, applying the non-constitutional Kotteakos standard to assess prejudice.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether excluding Wynn's testimony was error	Smith argues Wynn's testimony was relevant to demonstrate investigative shortcomings and alternative fingerprint methods.	United States contends the testimony was irrelevant, cumulative, and would confuse jurors.	Yes; exclusion was error.
Whether exclusion violated the Sixth Amendment right to present a defense	Smith asserts the defense could not fully present its theory without Wynn's testimony.	Government contends cross-examination sufficed to present defense theory.	Yes; rights were violated.
Whether the error was harmless under Kotteakos	Exclusion likely affected the verdict given the weak government case and lack of counterevidence from a defense expert.	Error was harmless since cross-examination and other evidence sufficed.	No; error not harmless; reversal required.

Dyas v. United States, 376 A.2d 827 (DC 1977) (test for admission of expert testimony; relevance and helpfulness to jury)
Jackson v. United States, 768 A.2d 580 (DC 2001) (feasibility of recovering fingerprints relevant to defense theory)
Kotteakos v. United States, 328 U.S. 750 (Supreme Court 1946) (harmless-error standard for non-constitutional errors)
Benn v. United States, 978 A.2d 1257 (DC 2009) (trial court broad discretion in admitting expert testimony; need for helpfulness)
Greer v. United States, 697 A.2d 1207 (DC 1997) (reasonable doubt standard and probative value of evidence)
Johnson v. United States, 398 A.2d 354 (DC 1979) (abuse of discretion in evidentiary rulings and impact on defense)
Wheeler v. United States, 930 A.2d 232 (DC 2007) (jurors’ role to independently weigh evidence)
Smith v. United States, 389 A.2d 1356 (DC 1978) (concerns about expert testimony influencing jurors)
Heath v. United States, 26 A.3d 266 (DC 2011) (contextual reference to harmless error standard (note: included for authority lineage))
Genuine Williams v. United States, None (N/A) (Not cited in opinion; placeholder to indicate no additional authorities)