In an apparent attempt to defuse reports of tension between the FBI and New York Police commissioner Ray Kelly, Mueller said, "New Yorkers are well benefited by the work of the NYPD and Ray Kelly."
Several of Zazi's friends who were taken into custody arrested and released during the raids told ABC News that authorities have it all wrong.
"He was a very nice person," said Naiz Khan, a coffee cart operator in Manhattan who is an acquaintance of Najibullah and attended the same mosque as him in Flushing, Queens. "He's not dangerous, he's a kid. So he can't be dangerous."
Khan, an Afghan native, was arrested Monday but released after four hours with no charges.
Heavily armed police believed they might find a bomb-making facility during their raids, but no bomb-making materials were discovered, auithorities told ABC News.
Asa Eslocker and Jason Ryan contributed to this report.