During the September 11, 2001 attacks on the World Trade Center, FBI agent Leonard W. Hatton Jr. was killed during the rescue effort while helping the rescue personnel evacuate the occupants of the South Tower and stayed when it collapsed. Within months after the attacks, FBI Director Robert Mueller, who had been sworn in a week before the attacks, called for a re-engineering of FBI structure and operations. He made countering every federal crime a top priority, including the prevention of terrorism, countering foreign intelligence operations, addressing cyber security threats, other high-tech crimes, protecting civil rights, combating public corruption, organized crime, white-collar crime, and major acts of violent crime.

Answer this question, if possible (if impossible, reply "unanswerable"): Who was sworn in as FBI Director a week after the attacks?
unanswerable