WASHINGTON (AP) — The FBI has been reviewing the handling of thousands of terrorism-related tips and leads received over the past three years to make sure they were properly investigated and no obvious red flags were missed.

The Associated Press has learned the review follows attacks by people who were once on the FBI's radar but who, in the past 12 months, have been accused of violence in an Orlando, Florida, nightclub, on the streets of New York City and at a Florida airport.

In each case, it was determined the suspects didn't require continued law enforcement scrutiny months and sometimes years before the attacks.

The review is an acknowledgment of the FBI's challenge in predicting which of the thousands of tips received annually might one day materialize into a viable threat.

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