Reports that three of the London suicide bombers visited Karachi will not come as a surprise to anyone. Pakistan's largest city is the place where the American reporter Daniel Pearl was kidnapped and beheaded on camera by militants believed to be linked to al-Qa'ida.
Karachi has a reputation for violence, so much so that the England Cricket Board is reportedly refusing to let its team play a Test match in the city later this year, citing concerns for the safety of the players. Bombs go off a little too often for comfort in Karachi and there is a high rate of drive-by shootings. On Sunday a senior Muslim cleric was killed when gunmen opened fire on his car from a motorbike.
Most of the violence has little to do with international Islamic militancy. It is fuelled by Pakistan's own sectarian conflicts. But the backdrop of lawlessness has allowed Islamic militancy to flourish.
Karachi is home to the Binori Town madrassa, one of the most famous jihadi madrassas and a place with overt links to Osama bin Laden. It used to be headed by Maulana Nizamuddin Shamzai, who was said to have been Bin Laden's spiritual mentor until Shamzai was assassinated last year. The Binori Town madrassa was one of the first places in Pakistan where the jihad against the Soviets in Afghanistan was preached, and where volunteers were recruited. The city made the international headlines when Pearl was murdered there in 2002. Unable to arrange his abduction in the better policed Islamabad, where Pearl was staying, his kidnappers lured him to Karachi with the promise of an interview with an elusive Islamic cleric.
His abduction tells us a lot about Karachi. He met his kidnappers in a crowded area in the centre of town, which was safe. He was driven to the suburbs, which were not. Police have lost control of the suburbs, and they were unable to track Pearl down, even though he was held in the city for some time before his murder. The man who arranged it was a Briton of Pakistani origin: Omar Saeed Sheikh.
Pakistani intelligence has named Qari Usman as one of five men arrested over the weekend in connection with the London bombings, and said he was an associate of Amjad Farooqi, who was killed by Pakistani forces last year, and was also involved in the Pearl kidnapping.
Karachi was in the news again later in 2002, when Ramzi bin al-Shibh, a suspect in the 11 September attacks, was captured after a gun battle, after al-Qa'ida broadcast an interview with Bin al-Shibh and the alleged mastermind of 11 September, Khaled Sheikh Mohammed, believed to have been filmed in Karachi. When Sheikh Mohammed was captured in Rawalpindi in 2003, there were reports that he had been in Karachi before moving north to evade capture. If the London suicide bombers did spend time in Karachi, it would have been easy for them to have made contact with Islamic militant groups.