Reporting from Islamabad, Pakistan – Security forces in the southern port city of Karachi have arrested Adam Gadahn, a Southern California native who became a top propagandist for Al Qaeda and is wanted by the U.S. on treason charges, Pakistani intelligence sources in Karachi said Sunday. The capture of Gadahn becomes the starkest signal yet that Pakistan has decided to ratchet up its cooperation with the U.S. in hunting down Islamic militants. In the last two months, Pakistani security forces have seized several top Afghan Taliban commanders, including the insurgency’s second in command, Mullah Abdul Ghani Baradar.