WASHINGTON (Reuters) - The controversial U.S. surveillance law known as FISA led to the discovery of a plot to attack the U.S. Capitol, House Speaker John Boehner said on Thursday, hinting that lawmakers may know more about how the FBI discovered the plan than court documents have revealed.

A federal court complaint filed on Wednesday indicated the FBI began monitoring 20-year-old Christopher Cornell after his Twitter posts indicated his support for the Islamic State.

Cornell then told an FBI informant that he planned to place pipe bombs inside U.S. Capitol buildings and shoot employees and officials inside, according to the court documents.

Boehner spoke at a press conference in Hershey, Pennsylvania on Thursday where he and Republican colleagues are meeting to discuss items on this year's legislative agenda, including reauthorizing the surveillance law known as FISA.

When asked about the foiled plan to attack the Capitol, Boehner said, "The first thing that strikes me, we would have never known about this had it not been for the FISA program and our ability to collect information on people who pose an imminent threat."