Ok, I'll try to explain a different way.
When you see a picture of the .22 with a silencer and sight fitted, why do you automatically assume it is the silencer containing the blood/DNA?
If the police used a silencer which they purchased themselves, it is a common product, I think Neil might have one, how does this damage the case against bamber?
Time and time again we see pictures and mike screams 'look' no exhibit label, look at how cross contamination happened, but how do you know it's the crucial silencer?