The following is a timeline of major events associated with the Sept. 11, 2001, attacks on the United States.
— Sept. 11: Terrorists hijack four jetliners and crash them into the World Trade Center, the Pentagon and a Pennsylvania field. The Twin Towers and Seven World Trade Center collapse.
— Sept. 13: Usama bin Laden identified as prime suspect in the attack.
— Sept. 14: Nineteen hijackers identified and linked directly to bin Laden.
— Sept. 17: Wall Street trading resumes, ending stock market's longest shutdown since the Great Depression. Dow loses 684.81 points, its worst-ever one-day point drop.
— Oct. 7: First airstrikes launched in Afghanistan. Bin Laden, in videotaped message, praises God for Sept. 11 attacks.
— Oct. 26: President Bush signs anti-terrorism bill giving police unprecedented ability to search, seize, detain and eavesdrop in pursuit of possible terrorists.
— Nov. 25: First wave of Marines lands near Taliban stronghold of Kandahar.
— Dec. 22: Hamid Karzai and his transitional government sworn in to lead Afghanistan.
— Feb. 14: Leaders of House and Senate intelligence committees announce joint inquiry of intelligence community's failure to prevent the attacks.
— Sept. 18: Investigator for joint inquiry testifies that intelligence agencies disregarded many warnings that terrorists might use planes as bombs.
— Nov. 25: Bush signs legislation creating Department of Homeland Security.
— Nov. 27: Bush signs bill establishing independent commission to investigate the Sept. 11 attacks.
— Dec. 11: Congressional inquiry issues final report on intelligence failures leading up to terrorist attacks. Key recommendations include creating Cabinet-level director of national intelligence.
— Dec. 13: WTC death toll drops to 2,792, one of several drops since the first anniversary of the attacks.
— Jan. 1: Thousands of newly hired government workers begin screening every checked bag at the nation's commercial airports for explosives.
— Jan. 27: The independent 9/11 commission, headed by ex-New Jersey governor Thomas H. Kean, launches its 16-month investigation.
— Feb. 19: Moroccan student Mounir el Motassadeq receives the maximum 15-year sentence in Germany for helping Sept. 11 hijackers. It was the first conviction tied to the terror plot.
— Feb. 27: Architect Daniel Libeskind's Freedom Tower plan, including a 1,776-foot spire and sunken memorial, chosen for rebuilding trade center.
— March 3: Design announced for Pentagon memorial, with 184 benches — each placed over an individual reflecting pool — inscribed with a victim's name.
— March 31-April 1: The 9/11 commission holds first public hearings, a half mile from ground zero.
— May 7: Federal investigators report that fireproofing on the WTC's steel floor supports was never tested and might not have met city building code.
— Aug. 28: The Port Authority releases 2,000 pages of transcripts from emergency calls and radio transmissions following attacks.
— Nov. 6: Firehouse across from World Trade Center re-opens.
— Jan. 23: The New York City Medical Examiner places final death toll from trade center attacks at 2,749.
— June 16-17: 9/11 Commission concludes 20 months of investigation with a preliminary report that fails to find "credible evidence" of Iraq and Al Qaeda collaboration on attacks.
— July 22: 9/11 Commission delivers final report to President Bush; its key findings include the failure of the Bush and Clinton administrations to make anti-terrorism a top priority.
— Dec. 17: Bush signs Intelligence Reform Act, a historic overhaul of the national intelligence system.
— March 24: Court ruling orders New York and its Fire Department to release tapes and transcripts of post-attack interviews with city firefighters, along with 911 calls from department personnel.
— April 22: Zacarias Moussaoui, the only person indicted in the U.S. for the attacks, pleads guilty to conspiring with the Sept. 11 hijackers. He faces the death penalty at a hearing next year.
— July 25: Former 9/11 Commission members give government "mixed grade" in following through on the panel's year-old recommendations.
— Sept. 7: A design is chosen for the Flight 93 National Memorial in Pennsylvania. The design pays tribute to the heroic struggle by passengers who thwarted an attack on the nation's capital.