Just some advise. Being that I have a bit of experience with this, I was primary team sniper for several years and now have given that spot up and am currently the Team Leader/Sniper Coordinator for our local jurisdiction so just take it for what its worth. Hopefully someone else in the field will chime in as well........
#1 I'm not sure where you are from but be very careful in building "Custom Guns" for this. Speak with your smith about it prior, to make sure he is capable, has detailed records including past and current builds including his accreditation and training. This will come into play whenever something "Off" the shelf is used in an actual shooting scenario. Be clear with him about the rifle's intended purpose as well as the fact he may need to be called in to testify in the event of a shooting or worse, some malfunction that leads to tragedy.
#2 Be real with your rifle's intended purpose. LEO Snipers do not take headshots at a 1000 yards, we leave that to the boys serving in our armed forces. Our shots tend to be very close, most if not all will be within 150 yards. So that said, super uber powered scopes are a hindrance at these ranges. It is much more about being able to place that shot on target 100% of the time, under various conditions including shooting at moving targets, hostage incidents, shooting through glass and in inclement weather conditions, you get the idea.
#3 If in fact you do pull the trigger on a suspect, your rifle along with all your Dope books will be collected, booked into evidence and retained until trial and any pending civil litigation closes. So be prepared to part with your baby for sometime after the shooting occurs.
#4 Now I may get slammed for this but in my opinion keeping the intended purpose in mind, I feel you would be much better served to just buy a tried and true factory sniper rifle system. A factory Remington 700 PSS, FN brand or equivalent will not be the best choice for 1000 yards but will more than suffice for your purpose. Put a 3.5x10 Leupold Mk4 and shoot factory match ammo and you will be fine. I would steer clear of anything much over a 308.
#5 Also remember since that is your assigned/personal rifle, you are responsible for what happens to it. Meaning, maintenance, repair and any adjustments will need to be made either through the smith you choose or your department's certified armorer. By going custom they may not be able to provide this for you.
Sorry for the long thread, I would hate to see you spend a butt load of cash only to find out something later. It may be different in your local area, as I work in Northern California, however police civil suites are nationwide. They are costly, take for ever and are very stressful to go through, trust me..........
On a side note, what state/agency do you work for and good luck at Sniper Schools, they are a kick in the ***.