The New York Times reports:

The Federal Bureau of Investigation is permitted to include people on the government’s terrorist watch list even if they have been acquitted of terrorism-related offenses or the charges are dropped, according to newly released documents.

The files, released by the F.B.I. under the Freedom of Information Act, disclose how the police are instructed to react if they encounter a person on the list. They lay out, for the first time in public view, the legal standard that national security officials must meet in order to add a name to the list. And they shed new light on how names are vetted for possible removal from the list.

Inclusion on the watch list can keep terrorism suspects off planes, block noncitizens from entering the country and subject people to delays and greater scrutiny at airports, border crossings and traffic stops.

The database now has about 420,000 names, including about 8,000 Americans, according to the statistics released in connection with the 10th anniversary of the Sept. 11 attacks. About 16,000 people, including about 500 Americans, are barred from flying.

Timothy J. Healy, the director of the F.B.I.’s Terrorist Screening Center, which vets requests to add or remove names from the list, said the documents showed that the government was balancing civil liberties with a careful, multilayered process for vetting who goes on it — and for making sure that names that no longer need to be on it came off.

“There has been a lot of criticism about the watch list,” claiming that it is “haphazard,” he said. “But what this illustrates is that there is a very detailed process that the F.B.I. follows in terms of nominations of watch-listed people.”

Still, some of the procedures drew fire from civil liberties advocates, including the Electronic Privacy Information Center, which made the original request and provided the documents to The New York Times.