Answer:
Osama bin Laden's Al Qaeda network.
Step-by-step explanation:
The investigation of US authorities determined that Al Qaeda, a terrorist network based in Afghanistan and other countries of the Middle East , was responsible for the 9/11 attacks. Its top leader was a Saudi man, an extremist named Osama Bin Laden, who was accused of masterminding the terrorist action on American soil. Bin Laden was killed in a commando raid by US agents in Pakistan in 2011, under the Obama administration.