Because there was no interviews after Bambers arrest on 29th September 1985, it allowed EP / the relatives / and Lab documents / and witness statements to be altered, making all the different silencers, SBJ/1, DB/1 and DRB/1, into one and the same silencer...
They were allowed to make all these alterations, between 29th September 1985, and October 1986, in time for the prosecutions to rely upon the Bamber (DRB/1) silencer / blood / paint argument as part of its case...
Why wasn't Bamber interviewed, and given an opportunity to explain about the silencers and the blood and the paint, before EP charged him with the murders?
If Bamber had been interviewed and the silencer / blood / paint evidence had been put to him at that stage, he would have alerted the police to the fact that several of the relatives all had identical Parker hale silencers, and that the blood / paint evidence being referred to may have been found upon or inside a silencer belonging to one of them...