Even as U.S. officials take satisfaction over the killing early Friday of Anwar al-Aulaqi in Yemen, they are outlining a strategic and legal policy to guide the use of drones against Al Qaeda leaders such as Aulaqi who are operating from new havens far from Pakistan.

A White House official responded to a call Friday morning emphatically: “It’s a good day for America.” He went on to summarize the rules of engagement that apply in the Aulaqi attack — and in the broader campaign against Al Qaeda’s far-flung affiliates.

The essence of the drone-attack policy, the official explained, is that the U.S. will target Al Qaeda affiliates if they are linked to the core group and pose a threat to the U.S. homeland. Group such as the Al-Shabab in Somalia, which have loose links with Al Qaeda, will be targeted only if they pose an external threat; if their battles are purely internal, drone attacks aren’t appropriate, policymakers have concluded.

The White House official also argued that the very process of mounting attacks against the U.S. — requiring travel, communication, and perhaps use of cell phones and other electronic devices — will make Al Qaeda operatives such as Aulaqi vulnerable in the countries where they are trying to operate. “If you are focused externally on the U.S. and operating in an external threat capacity, we are going to find you,” the White House official said.

The White House official presented some of the evidence that, in the view of the Obama administration, made Aulaqi a legitimate target for killing, even though he is an American citizen. A fact sheet prepared by the National Counter-Terrorism Center described him as “chief of external operations” for Al Qaeda on the Arabian Peninsula (AQAP) and said he played a “significant operational role” in the Christmas 2009 attempted bombing of a Northwest Airlines flight by Umar Farouk Abdulmultallab. According to the fact sheet, “Aulaqi specifically instructed Abdulmutallab to detonate the device while over U.S. airspace to maximize casualties.”

The intelligence document released by the White House also described Aulaqi’s alleged role in the October 2010 cargo-bomb plot: “Aulaqi had a direct role in supervising and directing AQAP’s failed attempt to bring down two U.S. cargo aircraft by detonating explosives concealed inside two packages mailed to the United States,” the document said. As part of this plot, Aulaqi allegedly communicated in January 2010 with Rajib Karim, a British Airlines worker, in an attempt to recruit operatives at Heathrow Airport in London to help with the attacks. Karim was convicted in a British court last March on terrorism charges.

U.S. officials insist that Aulaqi was a legitimate target under U.S. and international law because of his role as an operational planner in the group targeted by the authorization to use force against Al Qaeda and affiliates, which was passed by Congress on Sept. 18, 2001. The U.S. could also claim, under international law, that it was acting in self-defense, given its intelligence about Aulaqi’s role in planning attacks against America.

The evidence released this morning by the White House put Aulaqi on a list of approved targets, which is compiled by the CIA’s Counter-Terrorism Center and vetted by agency lawyers and the White House counsel’s office. In Aulaqi’s case, because he is an American citizen, there was also a broader review by the principals of the National Security Council, including the attorney general. The attack was a coordinated operation involving both the CIA and the military’s Joint Special Operations Command, in the Centcom area of operations.

It has been clear in recent days that the U.S. surveillance dragnet was closing in on Aulaqi. Defense Secretary Leon Panetta had signaled early last week that the drone war was moving to Yemen and AQAP, for which Aulaqi had been such an effective planner and propagandist.

The hunt for Aulaqi intensified as the U.S. and Yemen gathered information about Aulaqi’s movements. Officials spoke of significant gains over the past two weeks. By Thursday, American officials appeared confident that some major success in Yemen was imminent.

Aulaqi’s death was announced with a discreet note from the Yemeni Foreign Press Office at 5:30 a.m. Friday, with the subject line, “Breaking News.”