According to American

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 counter-terrorism

Counter-terrorism

Counter-terrorism is the practices, tactics, techniques, and strategies that governments, militaries, police departments and corporations adopt to prevent or in response to terrorist threats and/or acts, both real and imputed.The tactic of terrorism is available to insurgents and governments...

 analysts the Al-Matar complex was an Afghan training camp

Afghan training camp

An Afghan training camp is a camp or facility used for militant training located in pre-2002 Afghanistan. At the time of the September 11, 2001 attacks, Indian intelligence officials estimated that there were over 120 training camps operating in Afghanistan and Pakistan, run by a variety of...

 run by al Qaeda.

In 1999, Mohammed Atef

Mohammed Atef

Mohammed Atef was the alleged military chief of al-Qaida, although his role in the organization was not well known by intelligence agencies for years...

 met repeatedly with Bin Laden and Khalid Sheikh Mohammed at the Al-Matar complex to discuss possible targets for the 9/11 attacks.

According to testimony offered at the trial of Zacarias Moussaoui

Zacarias Moussaoui

Zacarias Moussaoui is a French citizen who was convicted of conspiring to kill citizens of the US as part of the September 11 attacks...

, Abu Turab al-Urduni

Abu Turab Al-Urduni

The son-in-law of Ayman al-Zawahiri, Abu Turab al-Urduni is a Jordanian who has been described by the United States government as one of five individuals who were aware of the operational details of the September 11th attacks. The other four being Osama bin Laden, Khalid Sheik Mohammed, Ramzi bin...

 -- the son-in-law of Ayman al-Zawahiri

Ayman al-Zawahiri

Ayman Mohammed Rabie al-Zawahiri is an Egyptian physician, Islamic theologian and current leader of al-Qaeda. He was previously the second and last "emir" of the Egyptian Islamic Jihad, having succeeded Abbud al-Zumar in the latter role when Egyptian authorities sentenced al-Zumar to life...

 -- provided training to the "muscle" hijackers at the al-Matar complex.
He was alleged to have provided training in how to disarm air marshal

Air Marshal

Air marshal is a three-star air-officer rank which originated in and continues to be used by the Royal Air Force...

s, in physical fitness and in basic English phrases. He also alleged to have provided them in training in truck bombings, in blowing up buildings, and in hijacking trains.

Mohammed Zarnuki's Summary of Evidence memo

Summary of Evidence (CSRT)

Counter-terrorism analysts prepared a Summary of Evidence memo for the Combatant Status Review Tribunals of the 558 captives who remained in the Guantanamo Bay detention camps, in Cuba in the fall of 2004.-The 2005 release:...

 asserted:

"A source identified Usama bin Laden's compound in Kandahar, Afghanistan called al Matar, which meant the airport." "A source identified al Farouq Al Farouq training camp The Al Farouq training camp, also known as "the airport camp", was an alleged Al-Qaeda training camp near Kandahar, Afghanistan. Camp attendees received small-arms training, map-reading, orientation, explosives training, and other training.... , al Matar and Aynak as the three al Qaida military training camps."

Faiz Mohammed Ahmed Al Kandari

Faiz Mohammed Ahmed Al Kandari

Fayiz Mohammed Ahmed Al Kandari is a Kuwaiti citizen who has been detained in Guantanamo Bay since 2002. He has been charged with war crimes.The US Department of Defense reports he was born on June 3, 1975 in Kuwait City....

faced the allegation:

"An individual stated that the detainee took a course in snipe-shooter training at the Airport Training Camp near Qandahar, Afghanistan."