So do the brown-stained pants of the cashier...were they confiscated and locked up, too?
There is "evidence"; and there is "reasonable evidence"; then there is this kind of "reasoning": the gun has to be used to prove that this guy was there as a witness, or his testimony is no good.
Where is the similar "evidence" similarly linking ALL THE OTHER WITNESSES? Where does it end?
I don't know what other evidence they have or need. And neither do you. What is the judge's history on what he accepts as evidence? What is the local Defense Attorney's tendency and record to defend these cases?
I answered the common question you asked and the common response that seems to be legally acceptable. It's a chain of evidence that makes all evidence stronger. If we assume that a jury is logical and can make reasonable inferences about the legitimacy of evidence and testimony....you get the point.
It's not that uncommon for the prosecution to hold useless evidence because they are afraid of what they might need unexpectedly later.
I am not supposing it's right or necessarily wrong. I don't know all the information. Oddly, this is at least the 4th time the police have confiscated his weapon as evidence. That pistol has apparently put a lot of bad guys in jail. Maybe it's good luck for the LEO to hold on to it. They should name this man's weapons Rabbit Foot.