I agree with Sgt. Lumpy about recording gun information. This is especially true for German Lugers and P.38's, where many guns can have the same serial number, and registration/sales records often show only the number, not the suffix, maker or date. If a Luger seized in a crime has that number, the legal owner(s) of every Luger with that serial number will be questioned.
And that often doesn't help the innocent person. During the investigation of the so-called "beltway sniper", a MD county police force seized every .223/5.56"assault rifle" in their files (such guns had to be registered at sale) for "investigation". In cases where the police found a woman at the home and the gun belonged to her husband (or SO), they made every effort to get her to surrender the weapon*; a surprising number did so with unknown results when the man came home and found his wife/SO had turned his gun over to the police for destruction.
*Community property state.