WASHINGTON — 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.