Kevin Johnson, USA TODAY
WASHINGTON (USA TODAY) - Twelve years after the Sept. 11 suicide hijackings killed nearly 3,000 people, outgoing FBI Director Robert Mueller said the terror scenario he fears most remains an attack on an aircraft.
Mueller, in a rare briefing with reporters before his scheduled departure Sept. 4, said officials were "lucky'' to have avoided tragedies when bombs in planes in 2009 and 2010 - one planted in the underwear of a passenger and the others rigged in printers that were being transported on cargo aircraft - failed.
"My biggest worry is an attack on a plane,'' said Mueller, who began his tenure the week before the most deadly attacks on U.S. soil.
In a wide-ranging discussion, Mueller, the longest-serving FBI director since J. Edgar Hoover, said the bureau faces substantial challenges in the coming months:
•Governmentwide budget cuts that will probably force agent furloughs.
• The increasing menace posed by cyber-threats, both as part of individual terror campaigns and the technology's application to the battlefield.
• The unpredictable nature of attackers acting alone, from the Fort Hood massacre to the Boston Marathon bombings, and the grim reality that those types of assaults will "probably be replicated.''
Agents, he said, are encountering investigative hardships caused by the unauthorized disclosures of once-secret surveillance tactics by the National Security Agency.
Mueller said the leaks by former National Security Agency contractor Edward Snowden, who was granted asylum in Russia this month to protect himself from federal prosecution in the USA, are "in the process of impacting'' terror investigations around the world.
The director declined to elaborate on those investigations. He has repeatedly asserted in recent congressional testimony that the controversial surveillance programs, including one that collects millions of U.S. citizen's telephone records, are important to the government's counterterrorism strategy.
Mueller, who helped transform the bureau after 9/11 into an intelligence-driven agency aimed at preventing terror attacks, said counterterrorism will remain the agency's "No. 1 priority for the foreseeable future.''
Briefly reflecting on the stunning events of Sept. 11, 2001, Mueller remembered it starting as a "beautiful day'' that quickly turned cataclysmic when jets plowed into the World Trade Center.
"It was very clear that it was a terrorist attack at that juncture,'' Mueller said of the event that changed his and the agency's mission forever.
"Bob will be known as the most transformative director in the history of the FBI since Hoover,'' former Homeland Security secretary Michael Chertoff said in a recent interview. "And I mean that in a good way.''
Until the deadly Boston Marathon bombings in April, Mueller and other national security officials had presided over more than a decade without a mass casualty bombing attack - although that long respite was aided by good luck: In separate incidents, commercial airline passengers swarmed attackers in 2002 and 2009 when explosives, one concealed in a shoe and another in underwear, failed to detonate on flights heading for the USA.
In 2010, a plot to bomb cargo planes destined for the USA with explosives hidden inside printer cartridges was averted when Saudi intelligence officials tipped U.S. authorities to the operation.
"Any one of those could have been a devastating attack, and we were lucky that they failed,'' the director said.
Mueller acknowledged the deep pain caused by the recent Boston bombings that killed three and wounded more than 200 others and the Fort Hood shooting in 2009 that left 13 dead and injured 30 more.
Both incidents, the director said, are emblematic of some of the most difficult counterterrorism challenges the bureau faces: foiling plots launched by so-called lone wolves with no apparent connection to terror organizations.
"You have one metric,'' Mueller said, "preventing all attacks. If there is one attack, you are unsuccessful.''
For Mueller, the final days in the last government job he is likely to hold begin next week when his successor, former deputy attorney general Jim Comey, comes to the bureau to begin the formal transition process.
Mueller said they will spend "most of the next week together'' in what is a rare transfer of leadership, having a current director in place to direct a transition.
"He'll be ready to go Sept. 5,'' Mueller said.
Mueller said he won't retire completely.
There will be speaking engagements, teaching assignments and private investigations to run.
"The time has come,'' he said. "It's time to let someone else in.''