This story makes a point that I've touched on several times:
WASHINGTON (AP) - More than 700 people were arrested on immigration violations and thousands more subjected to FBI interviews in an intense government effort to avert a terrorist attack aimed at disrupting the election.The uncertainty that is necessarily involved here is what causes so many problems. For all we know, the FBI might just have arrested someone who was about to commit a terrorist act. But up to now, that person might not be guilty of anything more than immigration violations (just as could have been said of the 9/11 hijackers on 9/10). On the other hand, all these folks could be completely innocent, just in the wrong place at the wrong time, etc.
As with past unrealized al-Qaida threats, law enforcement officials said Thursday they don't know for sure whether any of those arrests or interviews foiled an attack.
"It's very hard to prove a negative," Michael Garcia, chief of Immigration and Customs Enforcement, said in an interview Thursday. "We did cases and operations for people we thought posed national security concerns. We didn't arrest anyone who had a bomb."