U.S. Says It Didn't Target Muslims

In addition, documents discovered in Afghanistan indicated that terrorists could possibly use a U.S. mosque to hide radioactive material, said Jack Cloonan, a former FBI counterterrorism agent.

Cloonan, who earlier was interviewed by ABC News about the program, said it was not clear which mosques might have been considered.

The official familiar with the program acknowledged that "now it sounds like a crazy thing. But at the time it didn't sound like a very crazy thing. . . . All the intel was saying, 'An attack is coming, it's likely to be al Qaeda, likely to be launched in a U.S. city, likely to involve a dirty device'. . . . Where would you go looking for that?"

Authorities determined that in the past, al Qaeda terrorists or people close to them tended to live in Muslim neighborhoods or attend local mosques, the official said. That's how some sites became included in a program, he said. Other sites were chosen because of specific intelligence information.

Most of the testing was apparently done from nearby streets. But, according to U.S. News & World Report, in as much as 15 percent of the cases, officials had to go onto private property, such as mosque parking lots and private driveways, to get accurate readings.

Officials involved with the program said no warrants were needed because they were in public access areas. But some Muslim activists said they were concerned.

"We'd like our federal law enforcement agencies to know the American Muslim community stands firmly behind protecting our nation's borders," said Arsalan Iftikhar, legal director of the Council on American-Islamic Relations, one of the groups that are seeking the addresses of the sites involved. "But, at the same time, we are not willing to give up our guaranteed constitutional and legal rights in order to do that."

He said his group constantly received phone calls from Muslims who believed they were under surveillance. But none had specifically mentioned possible radiation testing.

U.S. News & World Report said that some officials believed the program, which involved property occupied or owned by U.S. citizens, was legally questionable. It quoted one unidentified source as saying that participants who complained "nearly lost their jobs."

Mason said that did not occur in the local FBI office.

"No one in the Washington Field Office would ever be so threatened," he said. "Never."