Incite Insight, what you wrote is true in accepting the logical train of thought. But most criminals are not in the habit of loaning out their piece around the neighborhoods, even among his fellow offenders. If one gun did killed five people.....then this fellow who had it with him, did all the killing.  Only way this theory can be wrong is if this guy stole the gun from the original killer, which states that we still do have a serial killer on the loose.