As has been previously said, it’s not just the police that walk through security checks, a number of other groups do likewise. Immigration officers (IO’s) – even if the items they are carrying set off the metal detector they are allowed through un-challenged and un-searched. Similarly, customs people. In T3 most don’t even enter via the “normal” staff route as far as I can see and never go near a metal detector. They may be more highly vetted, but that doesn’t stop someone dear to them being held hostage unless they take item X airside for some group of nutters. Please don’t think I am against either of the above groups, I’m not. It is the rules that allow them to do this that need to be looked at, the groups concerned are only complying with the rules.
Finally, I’ve never seen the point in putting flight deck crew through the security loop at airports. None would need a gun or knife to crash the aircraft – they already have that ability in their hands/heads. It was introduced, as far as I recall, so they were leading from the front as an example to cabin crew. If flight deck crew lead from the front by example, shouldn’t IO’s and customs be doing the same thing?