FBI Director Robert Mueller on Thursday defended a pair of controversial government surveillance programs, telling Congress that leaking information on them harms national security.

In his last appearance as FBI director before the House Judiciary Committee, Mueller said that terrorists track leaked information "very, very closely" and that because of leaks "we lose our ability to get their communications" and "we are exceptionally vulnerable."

"As to the individual who has admitted making these disclosures, he is the subject of an ongoing criminal investigation," Mueller said without naming Snowden.

Mueller added: "We are taking all necessary steps to hold the person responsible for these disclosures."  

Responding to questions by committee chairman Rep. Bob Goodlatte, R-Va., Mueller said the Foreign Intelligence Surveillance Court has approved the surveillance programs and they have been conducted in compliance with U.S. law and with oversight from Congress.

The revelation that the National Security Agency is collecting millions of U.S. phone records along with digital communications stored by nine major Internet companies has touched off a national debate over whether the Obama administration, in its efforts to thwart terrorism, has overstepped proper bounds by using intrusive surveillance methods.

Rep. John Conyers, the committee's ranking Democrat, expressed concern that the two programs were too far-reaching.

"It's my fear that we are on the verge of becoming a surveillance state," said Conyers.

Mueller is nearing the end of his 12 years as head of the law enforcement agency that is conducting high-profile investigations of the Boston Marathon bombings, the attacks in Benghazi, Libya, that killed four Americans and leaks of classified government information. Mueller's last day on the job is Sept. 4.

On Wednesday, Goodlatte said that when it comes to national security leaks, it's important to balance the need to protect secrecy with the need to let the news media do their job.

The Justice Department revealed last month that it had secretly gathered phone records of The Associated Press and emails of Fox News journalist James Rosen in an effort to crack down on leakers of classified information.

In the past week, a 29-year-old contractor leaked National Security Agency documents on the agency's collection of millions of U.S. phone records and the NSA's collection of emails and other information that people transmit online to and from foreign targets.

That has touched off a national debate over whether the Obama administration, in its efforts to thwart terrorism, has overstepped by using intrusive surveillance methods.

"Over the past few years, we have witnessed troubling national security leaks and have learned that the Obama administration seems to be bending the rules in place that protect the freedom of the press in its investigations," Goodlatte said.

On Benghazi, Republicans accuse the administration of misleading the public about an act of terrorism in the heat of the presidential campaign by saying the Sept. 11, 2012, assaults on the U.S. diplomatic post grew out of spontaneous demonstrations over an anti-Muslim video. In the immediate aftermath, U.N. Ambassador Susan Rice described it as a "horrific incident where some mob was hijacked, ultimately, by a handful of extremists." The White House says Rice reflected the best information available while facts were still being gathered.

Goodlatte said the committee planned to find out more about the status of what the congressman called the FBI's "stalled investigation" in Libya.

GOP lawmakers also have questioned why the military couldn't get aircraft or troops to Benghazi in time to thwart a second attack after the first incident that killed U.S. Ambassador Chris Stevens. Four Americans, including Stevens, died in the attacks that took place several hours apart.

Regarding the Boston Marathon bombings, committee members want to know whether there was a breakdown in information-sharing between federal agencies, preventing the FBI from thwarting the explosions that killed three people and injured more than 260.

Russia's internal security service, the FSB, sent information to the FBI about now-deceased bombing suspect Tamerlan Tsarnaev in 2011. The Russians told the FBI that Tsarnaev, an ethnic Chechen Russian immigrant living in the Boston area, was a follower of radical Islam and had changed drastically since 2010. Because of a subsequent FBI inquiry, Tsarnaev's name was added to a Homeland Security Department database called TECS that is used by U.S. officials at the border to help screen people coming in and out of the U.S.

In January 2012, Tsarnaev traveled to Russia and returned to the U.S. in July. Three days before he left for Russia, the TECS database generated an alert on Tsarnaev. That alert was shared with a Customs and Border Protection officer who is a member of the FBI's Boston joint terrorism task force. By that time, the FBI's investigation into Tsarnaev had been closed for nearly six months because the FBI uncovered no evidence that he was tied to terror groups.

Tsarnaev died after a shootout with police four days after the April 15 bombings. His brother, Dzhokhar, was charged in the bombings and is recovering from gunshot wounds at a federal prison hospital in central Massachusetts.

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