By CNN's Paul Cruickshank
A senior al Qaeda operations planner killed in a CIA drone strike last week was for several years a resident of the United Kingdom, and was associated with extremists and their activities before returning to Pakistan, U.S. counterterrorism officials told CNN.
Although the U.S. officials did not elaborate on his links to UK radicals, they said the al Qaeda operative - Aslam Awan - was a 29-year-old Pakistani citizen identified in British court documents as part of a group of Islamist extremists living in the Cheetham Hill area of Manchester.
By 2006 those extremists were increasingly attracting the attention of British security services, according to the court documents.
Awan, who arrived in Britain around 2002 on a student visa, had moved into an apartment in Cheetham Hill with Abdul Rahman, a school friend from Pakistan. Murad Iqbal, a Pakistani citizen from Karachi, also moved into the apartment, according to the court documents.
Strongly committed to al Qaeda's cause, the trio had begun recruiting other young men in the Manchester area, taking them on camping trips in the Lake District in March and June 2006, where they simulated suicide bombing exercises, according to the documents. Home movies of their training that were played in court show them "leopard crawling" in the snow.
Their recruiting techniques were compared to a pedophile grooming a child.
Later in 2006, Awan set off for the Afghanistan-Pakistan border region to fight, according to British authorities.
But Awan wanted his radical Manchester circle to join him in Pakistan. He sent a letter to his school friend Rahman in Manchester, calling on him and the others to travel to Pakistan.
The letter, later found by police in Rahman's bedroom, referenced his terrorist training and described his participation in the fighting, according to the court documents. In the letter Awan also described visits to the graves of al Qaeda fighters and provided instructions for the distribution of CDs glorifying the group's exploits.
He wrote that the group needed assistance in combating "air power," and requested Iqbal contact a mutual friend about it.
According to the court documents, in October 2006, one of the young men being groomed by the group - Omar Arshad, who had dropped out of pharmacy studies at Manchester University - fell out with his family and was reported missing by his father, who told police he was concerned his son was being radicalized.
In January 2007, the documents state, his father tracked him down and brought him back to Manchester, where he was served with a "control order," a British legal mechanism strictly restricting the movement and communication of terrorist suspects in which there is not sufficient evidence to bring charges.
British police believed Arshad was planning to set off imminently for Pakistan for terrorist purposes.
Arshad went back to the Cheetham Hill apartment, where Rahman, Iqbal and others in the group hatched a plan for Arshad to escape, the court documents state. Arshad shaved his beard, and a member of the group drove him to Birmingham airport, where he caught a plane to Iran the next day. Rahman paid for the flight.
British authorities believe Arshad has now joined militants in Pakistan.
Later, Iqbal also traveled to the Afghanistan-Pakistan border region to join his friends, according to the documents. In November 2007, Rahman pleaded guilty to disseminating terrorist literature and aiding or abetting the breach of a control order.
The men in the Cheetham Hill group were also connected to Rangzieb Ahmed, a senior al Qaeda facilitator from the Manchester area who in 2008 was convicted in Britain for directing terrorism after being arrested in Pakistan. That connection emerged at Ahmed's trial.
Awan, for his part, appears to have been quickly promoted up al Qaeda's ranks as other operatives were killed in drone strikes.
Several others who spent significant time in the West have likewise been promoted to senior positions in the terrorist network.
They include Adnan Shukrijumah, a Saudi-born American who joined al Qaeda around 9/11 and who helped plan a suicide bomb attack on New York in 2009, according to U.S. officials. Like 9/11 mastermind Khalid Sheikh Mohammed, who attended an American university, their first-hand knowledge of Western countries has been an important resource for the terrorist group. Awan was working on attacks against the West when he was killed, another U.S official told CNN.
Half a dozen UK residents have been killed in drone strikes in Pakistan in recent years, including two from east London late last year. British authorities say that British militants are among hundreds of Europeans in Pakistan who are linked to, or training with, jihadist groups. In September, British police thwarted a terrorist plot by an alleged terrorist cell in Birmingham who trained in Pakistan in 2011.
CNN's Pam Benson contributed to this report.