The murdered man had been shot - twice. Either bullet could have caused the death.
D.A. Doug Selby had both the bullets and one of the guns. On that gun were the fingerprints of Pete Ribber, a known criminal. The other bullet was from a different - and missing - gun.
Which bullet had caused the death? That was the D.A.'s problem. Because there's no law against firing a bullet into a corpse ...