(CNN) -

Here is some background on the terrorist attacks of September 11, 2001.

Facts: On Sept. 11, 2001, 19 men hijack four fuel-loaded commercial airlines bound for West Coast destinations. This terrorist attack on the United States is orchestrated by al-Qaida leader Osama bin Laden. A total of 2,977 people are killed in New York City, Washington, D.C., and outside of Shanksville, Pa., in the worst terrorist attack in U.S. history.

The victims: At the World Trade Center site in Lower Manhattan, 2,753 people are killed when hijacked American Airlines Flight 11 and United Airlines Flight 175 are intentionally crashed in the north and south towers.

Of those who perish during the initial attacks and the subsequent collapses of the towers, 343 are New York City firefighters, another 23 are New York City police officers and 37 others are officers at the Port Authority.

The victims range in age from two to 85 years. Approximately 75-80 percent of the victims were men.

At the Pentagon in Washington, 184 people are killed when hijacked American Airlines Flight 77 crashes into the building.

Near Shanksville, 40 passengers and crew members aboard United Airlines Flight 93 die when the plane crashes into a field. It is believed that the hijackers crashed the plane in that location, rather than their unknown target, after the passengers and crew attempted to retake control of the flight deck.

Timeline:

Sept. 11, 2001

- 8:46 a.m. ET - American Airlines Flight 11 (traveling from Boston to Los Angeles) strikes the north tower of the World Trade Center in New York City.

- 9:03 a.m. ET - United Airlines Flight 175 (traveling from Boston to Los Angeles) strikes the south tower of the World Trade Center in New York City.

- 9:37 a.m. ET - American Airlines Flight 77 (traveling from Dulles, Va., to Los Angeles) strikes the Pentagon Building in Washington.

- 9:59 a.m. ET - South tower of WTC collapses in approximately 10 seconds.

- 10:03 a.m. ET - United Airlines Flight 93 (traveling from Newark, N.J., to San Francisco) crashes in a field near Shanksville.

- 10:28 a.m. ET - North tower of WTC collapses. The time between the first attack and the collapse of both World Trade Center towers is 102 minutes.

Dec. 13, 2001 - The U.S. government releases a tape in which Osama bin Laden takes responsibility for the attacks.

Dec. 18, 2001 - Congress approves a measure to allow the president to designate Sept. 11 as "Patriot Day" on each anniversary of the attacks.

Jan. 23, 2004 - The New York City Medical Examiners Office has issued 2,749 death certificates, the first time since the attacks that the number of death certificates has matched the number of victims.

June 15, 2004 - The Victims Compensation Fund finishes its work processing death and injury claims from families and relatives of Sept. 11 victims. Families of those killed had until Dec. 22, 2003 to apply for compensation. Families who agreed to get compensation from the federal fund agreed not to sue the airlines.

Feb. 22, 2005 - Saying it has exhausted all DNA technology, the New York City Medical Examiner Office halts the process of identifying human remains from the Sept. 11, 2001, terrorist attacks at the World Trade Center site. Of the 2,749 people known to have been killed at the World Trade Center site, only 1,585, or 58 percent, are identified by recovered physical remains.