A German citizen of Afghan descent was the source of much of the information on a potential "Mumbai-style" terror plot in Europe, a German counterterrorism official said Wednesday.

The man, Ahmed Sidiqi, was detained in Kabul in July and transferred to U.S. custody where he has "revealed details about the terror plot," said the official, who did not want to be named because he is not authorized to talk to the media.

The man and several other Germans traveled from Hamburg to the Afghan-Pakistan border area in 2009, where he joined the Islamic Movement of Uzbekistan, an extremist group allied with al Qaeda, German intelligence officials said.

Sidiqi, once captured, "started to talk a lot," and detailed a "Mumbai-style" attack in Europe, the German official said.

...The intelligence indicates there is interest in using people with Western passports in an attack, that official said. This source says the potential operatives may be a mix of Europeans and others possibly including North Africans, Pakistanis, Turks, Uzbeks, and Tajiks.

There is concern about an "active shooter" scenario that would create as many casualties and as much chaos as possible in a short period of time.

The Mumbai attacks showed how effective this kind of an attack can be in drawing attention.

According to this source, economic targets in Europe could be possible targets, including institutions such as banks and stock exchanges.

A separate law enforcement source said "the belief is" that Osama bin Laden signed off on a European attack plan, and that source confirmed the intelligence related to a Mumbai-style attack.

The German government is increasingly concerned about the number of Germans becoming jihadists. According to a senior German counterterrorism source, some 200 individuals have traveled to train with Jihadist groups in the Afghanistan-Pakistan border region since the 9/11 attacks.