Responsibility for the September 11 attacks

At around 9:30 pm on September 11, 2001, George Tenet, director of the Central Intelligence Agency (CIA), told President George W. Bush and U.S. senior officials that the CIA's Counterterrorism Center had determined that Osama bin Laden and al-Qaeda were responsible for the September 11 attacks. Two weeks after the terrorist attacks on September 11, 2001, the Federal Bureau of Investigation connected the hijackers to al-Qaeda, a militant Salafist Islamist multi-national organization.

Source: Wikipedia — Responsibility for the September 11 attacks (CC BY-SA 4.0)