“The concerns we have about individuals who may support terrorism being in the United States run from concerns about providing financing, radicalizing others,” Mueller said, as well as “the potential for individuals undertaking attacks in the United States.” “All of those are relevant concerns,” Mueller said. The FBI chief said he would not discuss specific individuals. He said there were also potential risks to putting detainees in maximum security prisons. Rep. Jerrold Nadler, D-N.Y., whose district includes the World Trade Center site, then prodded Mueller to agree that such individuals could be safely kept in maximum security prisons in the U.S. Mueller balked at Nadler’s suggestion, noting that in some instances imprisoned gang leaders have run their gangs from inside prisons. “It depends on the circumstances,” Mueller said.