Pointless nit-picking

One does question the need for all the relentless forensicking going on at the crime scene in London; the fingertip search in the area where the terrorist was shot especially. The killer is known, there’s no doubt about what he did and he’s dead so there isn’t going to be a trial. So what is the point of wasting a lot of time and money, which the Metropolitan police farce assures us is in very short supply, on doing things which will be just filed and never used?