The problem here is a fact that we have pointed out many, many times at Jihad Watch: there is no reliable way to distinguish jihadists from peaceful Muslims. There is no Islamic authority (with the arguable exception of the Spanish ulama) that has declared that Muslims who hold to the theology and ideology of Osama bin Laden are not true Muslims and are not welcome in their mosques. Making this even more difficult is the doctrine of religious deception founded on Koran 3:28. Thus the Afghan police authorities couldn't have kept Taliban loyalists out, even if it tried -- and it is unlikely that it is trying. This is something for the learned analysts to ponder not only as it concerns our policies in Afghanistan, but numerous other policies as well, including immigration, the language used in defending ourselves from this threat, and more.

"Five British soldiers killed by rogue Afghan policeman," from The Times, November 4 (thanks to Kris):

Five British soldiers have been shot dead after a rogue Afghan policeman opened fire inside a check point, [sic]

The soldiers, three from the Grenadier Guards and two from the Royal Military Police, died in the Nad-e'Ali district of Helmand Province yesterday afternoon.

It is thought a further three Afghan police officers were also killed and up to six men injured.

The soldiers had been stationed at the post for two weeks, alongside a detachment of Afghan police whom they had been mentoring.

The troops were inside a police checkpoint in Nad-e Ali when the policeman, named locally as Gulbaddin, launched his attack.

"Without warning one of the ANP (Afghan National Policemen), potentially in concert with another, picked up his weapon and started firing," a military official told The Times.

Officials said the gunmen fled the scene, possibly with his accomplice. It has been suggested the killer may have had links to the Taleban....

No kidding, really?