FBI chief Robert Mueller while defending the spy programme said that the 9/11 attacks could have been prevented had the Prism system was implemented earlier.
According to Guardian, Mueller vows to take strong action against whistleblower Edward Snowden who leaked the intelligence programme details about the government snooping on citizens' telephone records and web activities.
According to the report, Mueller said that the 'metadata' of phone records was extremely crucial for the security purpose and it would help prevent another 'Boston Bombing' attack.
Mueller further explained the necessity of tapping phone calls by giving the example of Khalid-e-Midhar, one of the 9/11 hijackers who had called a Yemeni safe house from a phone in San Diego before the attack. Mueller said that had the surveillance system been in place then, the attacks could have been foiled.
The report said that despite Mueller's defense for the snooping system, Congressmen are still not convinced about the system infringing the privacy rights of the citizens.
Republican Louis Gohmert also pushed back at the FBI, accusing it of over-classifying surveillance.
However, Mueller further insisted that even disclosure of the ways of the 'metadata' collection could help terrorists 'find ways around' and make US exceptionally vulnerable to attacks, the report added.