Patterson v. State, 146 A.3d 496

In July 1992 Rudolph Holland was fatally shot; several witnesses placed two men at or fleeing the scene, and some identified Patterson as one of them.
Patterson was arrested in D.C. on July 17, 1992; Officer Hyatt testified Patterson discarded a .38 revolver before arrest.
FBI Special Agent Williamson testified at trial that the bullet recovered from the victim was fired from Patterson’s seized .38 “to the exclusion of any other firearm in the world.” The prosecutor relied on that testimony in closing and rebuttal.
The jury convicted Patterson of first-degree murder and related handgun offenses; he received life plus a consecutive term.
In 2013 Patterson filed a petition for a writ of actual innocence challenging the reliability and admission of firearms comparative microscopic matching (toolmark identification), citing scientific literature and decisions criticizing emphatic identification claims.
After a hearing the circuit court denied the petition; the Court of Special Appeals affirmed, holding Patterson failed to show a substantial possibility the verdict would have been different given (1) toolmark identification remains generally accepted and (2) other inculpatory evidence at trial.

Issue	Patterson's Argument	State's Argument	Held
Whether the circuit court abused its discretion in denying a CP § 8-301 petition attacking firearms comparative microscopic matching testimony	The FBI expert’s unequivocal claim that the gun fired the fatal bullet was junk science; recent studies and cases would have undermined that testimony and created a substantial possibility of a different verdict	Comparative microscopic matching remains generally accepted and admissible; even if Williamson could not state absolute certainty, he could still give a reliable opinion and other evidence would still support conviction	No abuse of discretion: petitioner failed to prove a substantial or significant possibility of a different result

Fleming v. State, 194 Md. App. 76 (toolmark identification remains generally accepted and admissible)
Clemons v. State, 392 Md. 339 (Frye–Reed standard for scientific evidence admissibility)
Reed v. State, 283 Md. 374 (discussing disciplines generally accepted for judicial notice)
Yonga v. State, 446 Md. 183 (standard for showing substantial or significant possibility under CP § 8-301)
McGhie v. State, 224 Md. App. 286 (abuse-of-discretion review of actual innocence petitions; other evidence can defeat petition)
Ward v. State, 221 Md. App. 146 (contrast where newly discovered scientific evidence did require relief)