Being raised in the evil empire and being a police officer I can sort through the confusion.
The WB&TS has never written that Jehovah's Witnesses are prohibitted from being police officers. In fact, there was a Questions from the Readers article in 2002 that asked why a recent Awake! article protrayed police in a positive light when Witnesses cannot be police officers. The reply was: "We've never said that. However, if you're thinking of becoming one you should read this" and it had a footnote to an old Watchtower article.
Back in the very early 1980's a Watchtower article came out dealing with murder/killing. It statied that if you had a job the required you to carry a weapon to protect you from other people you had 6 months to find new employment or you would not be able to have any extended privileges in the congregation. I believe the reason for this is, if you were to kill someone, you would become bloodguilty, which is a disfellowshipping offense.
As a result, the mindless masses of Witnesses drew a false conclusion that Witnesses could not be police officers. The fact is just the opposite. Just forget about ever becoming a Ministerial Servant or an Elder. If you save a life, including your own, by fulfilling Romans 13:1-7 be prepared to be disfellowshipped due to a mis-translation of "Thou shall not murder" to "You should not kill" courtesy of the NWT.