No, it is not a waste of time. It is an illustration of just how few leads this case has. If an investigative agency is reduced to doing what is little more than a random gun canvas they cannot have any other way to go.
If I didn’t do it, I wouldn’t take my gun in.
They are essentially asking for innocent people to prove they didn’t do it. Just something hinky about that to me.
If they have so little to go on, my going in and proving that my gun did not do it doesn’t get them any closer to the killer.
And I am sure as hell not going to give anyone the chance to screw up and come to the erroneous conclusion that I did do it. Not going to happen.