A city of 13 million -- with some estimates of 100,000 new arrivals a month -- Karachi as seen an influx of Pashtuns from the tribal border region with Afghanistan. Many fled there during fighting and offensives in the Northwest Frontier Province and Waziristan, making it a comfortable place for the Taliban to blend in and count on a network of supporters.

1.3e7 people in one city?

1 megaton?

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His family has said they last heard from him in 2002. In 2004, the FBI identified him as part of an al Qaeda cell that was planning attacks aimed at disrupting that year's presidential election in the United States.

In October 2004, he began appearing in disguise in al Qaeda videos. Gadahn dropped the disguise in 2006.

In 2008, he renounced his U.S. citizenship and destroyed his passport in another al Qaeda video.

In his video message posted online Sunday, Gadahn says Muslims should emulate the alleged Fort Hood shooter.

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In December, Gadahn released a video message in English offering condolences to "unintended Muslim victims" killed in attacks in Afghanistan, Pakistan and elsewhere. It was a rare example of al Qaeda offering condolences to the families of those killed in the group's own attacks.

hmm.