Who was involved in 9/11

Terrorist groups performed a terror attack on the US

Many people were involved, including firefights, police, and of course medics. A lot of workers/employees were in the twin towers, causing the need of the people mentioned before. (This is more since I don't know exactly what you need), but they were faced with the choice to either jump or try to escape from the stairs. Many lives were lost during 9/11. It was caused by terrorist group Al Qaeda, and led by Osama - bin laden, who was later killed