which place did he attack?
He hijacked the American Airlines Flight 77.
Khalid al-Mihdhar
 He was one of the five hijackers of American Airlines Flight 77, which was flown into the Pentagon as part of the September 11 attacks.
what is khalid al-mihdhar? He was a Saudi Arabian Hijacker.
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Khalid al-Mihdhar [SEP] Introduction
Khalid Muhammad Abdallah al-Mihdhar (, ; also transliterated as Almihdhar) (May 16, 1975 – September 11, 2001) was a Saudi Arabian Hijacker. He was one of the five hijackers of American Airlines Flight 77, which was flown into the Pentagon as part of the September 11 attacks. Mihdhar was born in Saudi Arabia and fought with the Bosnian mujahideen during the Bosnian War of the 1990s. In early 1999, he traveled to Afghanistan where, as an experienced and respected jihadist, he was selected by Osama bin Laden to participate in the attacks. Mihdhar arrived in California with fellow hijacker Nawaf al-Hazmi in January 2000, after traveling to Malaysia for the Kuala Lumpur al-Qaeda Summit.