The charges announced Wednesday against five alleged members of an al Qaeda plot to attack the United States and the United Kingdom underline the evolving links between would-be jihadists in western countries and the vital importance of intelligence sharing.

The charges link Najibullah Zazi, who has admitted trying to bomb the New York subway, and people arrested last year on terrorism charges in Manchester, England, specifically a student there, Abid Naseer. There may also be a link to an alleged plot in Norway; three men have been arrested there in the past 24 hours.

The volatile tribal territories of Pakistan have become the nexus for would-be terrorists bent on attacking NATO forces in Afghanistan or, more frequently, receiving the training that would allow them to commit acts of terror at home. Two of the London 7/7 bombers, Bryant Neal Vinas, Faisal Shahzad, Najibullah Zazi, Abid Naseer and a substantial Belgian cell have all beaten a path to Pakistan and either al Qaeda or the Pakistani Taliban.

Zazi and Zarein Ahmedzay have pled guilty in the New York plot; a third man, Adis Medunjanin, has denied the charges and is scheduled to go on trial. They are all alleged to have gone to Pakistan in the second half of 2008.

Interceptions of e-mails by British intelligence may have helped uncover the links between the British and U.S. cases. The Daily Telegraph in Britain reported in November 2009 that UK intelligence had alerted the FBI to Zazi's presence in Pakistan.

The Telegraph's security correspondent Duncan Gardham wrote: "Security sources have told the Daily Telegraph that Zazi and the men arrested in Manchester were part of a complex network directed from Pakistan. They are reticent on how Zazi was identified but admit it was through an 'intercepted communication.'"

The network was uncovered following the arrest of U.S. national Bryant Neal Vinas in Pakistan last November. Vinas, 26, also known as Bashir al-Ameriki, claims he met Rashid Rauf, the British al Qaeda commander behind the trans-Atlantic bomb plot.

The intercepted communications were apparently from an al Qaeda facilitator named only as Ahmad in the Department of Justice complaint. He was allegedly in touch with both Zazi and Vinas, the subject of a recent CNN documentary "American al Qaeda." He was arrested in Peshawar late in 2008 and extradited to the United States, where, according to U.S. officials, he provided a treasure trove of information on his time in Pakistan.

As intelligence agencies on both sides of the Atlantic pieced together the suspects' movements. They began to learn who they may have met or communicated with. One senior al Qaeda operative appears to have directed their conspiracies: Adnan El Shukrijumah, who the United States says was a leader of al Qaeda’s external operations program.

The indictment says that El Shukrijumah recruited Zazi to conduct suicide bombings in New York with bombs made of hydrogen peroxide, acetone, flour and oil.

Shukrijumah, originally from Saudi Arabia, remains at large and is thought to be in Pakistan. Growing up, he lived in Brooklyn (where his father was an imam) and Florida and has a $5 million reward on his head. The indictment adds that he also recruited another of those charged on Wednesday, Adis Medunjanin, who in January allegedly tried to crash his car on the Whitestone Expressway in Queens, soon after an FBI raid on his home.

Shukrijumah and Medunjanin are charged with conspiring to use weapons of mass destruction, conspiring to provide material support to al Qaeda and giving and receiving al Qaeda military training.

But British police made one crucial misstep as they closed in on the alleged plotters in the spring of 2009, fearing an attack was imminent. A senior detective, assistant commissioner Bob Quick, was entering No. 10 Downing Street, the prime minister's residence, with a sheaf of papers. Clearly legible were details of the planned operation against the suspects, who were then living in Manchester and Liverpool. Quick subsequently resigned.

No bomb-making equipment was found, and the men were released without charge. The government subsequently tried to deport the men. In Naseer's case it failed: in May an immigration court allowed him to remain in Britain, even as it conceded he was a security risk.

Intelligence suggested Abid Naseer, 24, and his accomplice Ahmad Faraz Khan, 26, were planning a “mass casualty attack,” probably against shoppers in Manchester over the Easter holiday last year.

But the judges said Naseer and Faraz Khan, who came to Britain as students, should not be sent back to Pakistan because they could be tortured. The government was furious but powerless.

Now Naseer is under arrest again after being picked up in the north-east of England. He faces extradition to the United States.