The weekend attack by Al Qaeda and Taliban in Pakistan showed the lethal role Pakistani military defectors play in terrorism.
Saturday's joint Al Qaeda-Taliban attack on Pakistan's army headquarters, in the middle of one of Pakistan's most heavily fortified cities exposed the capacity of extremists to elude defenses and strike at the heart of the state.
But what is more of a setback for Pakistan's fight against militants is that the mastermind of that attack was an ex-military officer turned extremist: Mohammed Aqeel, also known as Dr. Usman, a nom de guerre he acquired while serving as a nurse in the Pakistan army's medical corps.
He is not alone. In recent months, as Pakistan's confrontation with extremists has escalated to record levels of violence, US and Pakistani military forces have arrested and killed several former or retired Pakistani military officers who are now aiding extremists. These men, trained by the military and privy to both its tactics and its security protocols, constitute one of the most dangerous threats in Pakistan's battle against militancy, and help to explain why Pakistan's insurgency has proved so lethally skilled and resilient.