The Central Office uses systematic research to investigate and assemble groups of connected crimes.

Four years ago, after the 9/11 attacks, a judge agreed to give the police greater powers to investigate political groups.

But there is another way to get the F.B.I. back into the business of investigating political groups.

The government has agreed to set up a commission to investigate clandestine groups suspected of being behind a wave of violence against human rights advocates.

The police were required to have "specific information" that a crime was in the works before investigating such groups.

Mr. Eisenstein and his colleagues said there must be safeguards in place when the police seek to investigate political groups.

They required the department to seek approval of a special panel to investigate political groups or activities.

Doubling the number of investigating groups also greatly increased the rate at which we could work.

But he said the city investigates religious groups only when the department gets complaints, and few are received.

German law imposes sharp restrictions on the ability of authorities to investigate religious groups.