Don't worry, it will be proven. I'm not sure but I think it may have been the poster " Martin " that also wrote about this in 2011 ?
The only way to prove the existence of it would be crime scene photos showing the Pargheter rifle on the premises.
Since 11 crime scene photos of the office and gun cupboard have been cut out from the film strips. Its probably impossible to confirm one way or the other.
If it was proven to be there, all it would prove is that the relatives have told yet more lies. So I don't really concern myself with it if that's all it can establish.