Who would you trust to assess the state of a crime scene, crime scene officers who are used to paying attention to detail or members of a raid team who are trained to focus on a target?
Depends on the issue. In the US all cops are trained to use guns and crime scene officers are trained about the finer aspects.
In the UK most cops don't use guns and thus are at a disadvantage when it comes to some firearms related issues. Hopefully now they are trianed much more about every aspect.
The raid team noticed the struggle in the kitchen as well as the lack of evidence on Sheila that should be present had she taken part in a struggle and shot people. The coroner and crime scene officers should have noticed these same things since the raid team did.
The coroner and crime scene officers seemed to ignore it. Vanezis later blamed this on not being shown the seen right away but none of his gun related claims were too bright. He stupidly suggested possibly someone stabbed Nevill with the barrel of the rifle and that this caused the marks. He said such at a point in time when he knew the moderator had been attached. Apart from the notion of being stabbed with the rifle barrel being stupid the moderator being attached should have told him it was a stupid suggestion. If he knew anything about the use of guns he would know people are hit with the butt of the rifle and the corner of the butt would be able to make marks like the gouges to Nevill's arms. He figured out the butt was used to bash Nevill's head in so you would think he would be able to figure out Nevill would have tried defending himself from such blows with his arm thus his arm getting gouged.
The lab helped save the case, otherwise a crappy job was done which is why the Dickinson investigation occurred. They wanted to try to find out what went wrong so they could try to prevent the same bad policing in the future.