Harry Samit is a Federal Bureau of Investigation Special Agent based at the FBI Field Office in Minneapolis, Minnesota. He is a former United States Navy Naval Intelligence Officer who participated in an aviation indoctrination course (he does not hold Naval Aviator wings). Samit's aeronautical ratings consist of an Air Transport Canada (Canadian) certified private pilot license. Samit is most noted for arresting Zacarias Moussaoui on August 16, 2001.
Samit became aware of Moussaoui because of Clancy Prevost, a certified flight instructor at the Pan-Am International Flight Academy in Eagan, Minnesota. Moussaoui had enrolled for training in a 747-400 flight simulator at the school on August 13 but his behavior during instruction alarmed Prevost, who did not believe that Moussaoui was just a wealthy individual interested in flying jumbo jets. At Prevost's urging, the flight school contacted the Minneapolis FBI Field Office, and Samit was one of the special agents assigned to investigate Moussaoui.
Moussaoui was arrested by INS Special Agents for a visa violation on August 16 but, because the arrest was effected outside the Residence Inn where Moussaoui had been staying, Samit had no legal right to search the hotel room and its contents without Moussaoui's consent. Moussaoui denied consent, so Samit could only search Moussaoui and his car. Samit found a small knife in Moussaoui's left pocket and another knife in the car.
As a certified private pilot himself, Samit was suspicious, suspecting that Moussaoui was plotting an act of international terrorism against the United States. He therefore sought permission to search Moussaoui's belongings which were known to include several bags and suitcases, and a laptop computer. The first application to obtain a criminal search warrant was denied by FBI Headquarters on the ground of insufficient evidence. A second application to search was made under the Foreign Intelligence Surveillance Act of 1978, but this was also denied. The FBI did obtain a search warrant for the belongings, but only after the September 11th attacks. The Minneapolis Field Office had received a report from Moussaoui's home government of France that linked him to Islamic terrorism, but the FBI Headquarters in Washington did not believe that evidence was sufficient to present to the FISA court for a search warrant. On the question of using foreign government intelligence to validate a request for a domestic search warrant through the FISA court, it is unclear if the Field Office could have appealed administratively to the White House National Security Council. Had the belongings been opened before September 11, knives, flight manuals, and other clues would have been found. Whether these clues would have sparked a national emergency or simply been treated like the August 6 memo entitled Bin Ladin Determined To Strike in US is subject to debate.
When FBI Headquarters denied both Samit's application for search powers, he initiated a process to notify the Federal Aviation Administration (FAA) of his suspicions of possible aircraft hijacking attempts, but FBI Headquarters censored the memo. Relying on personal contacts, Samit then met with a Minneapolis FAA official, but that official did not pursue Samit's leads.
"I am so desperate to get into his computer, I'll take anything," Samit wrote in an e-mail on September 10, 2001.
In March 2006, during Moussaoui's death sentence trial, Samit testified that he had spent the time between August 16 and September 11 trying to warn U.S. officials about the possibility of terrorist actions involving the hijacking of aircraft. Four such actions occurred in the United States on September 11, 2001. Samit testified under oath that "criminal negligence, obstruction and careerism"  by superiors at FBI Headquarters in Washington, DC thwarted an opportunity to prevent the September 11th attacks.
- The Grounded Man Rake Magazine May 2005, retrieved Feb 6, 2017
-  KTWB-TV, retrieved March 27, 2006
- Agent Faults FBI on 9/11 The Los Angeles Times March 21, 2006, retrieved March 27, 2006
- "September 11 alert was ignored, says FBI agent". The New Zealand Herald. March 22, 2006. Retrieved October 2, 2011.
- Moussaoui alerts ignored, agent says[permanent dead link] The Sacramento Bee March 21, 2006, retrieved March 27, 2006
- Freze, Colin (September 11, 2009). "Jailed Arab details ties to tortured Canadians". The Globe and Mail.