Minutes after the crash, first responders arrive on the scene, along with the Pennsylvania State Police. The September 11 attacks generate the largest investigation in FBI history. The primary goal of the investigation is to recover sufficient evidence to learn who committed the crime, how it was carried out, who financed the operation, and what might happen next.
Clues From Flight 93
Investigators quickly realize that of the four crash sites, the Shanksville location will likely yield the most evidence in the least amount of time. Because Flight 93 crashes in an open field, parts of the plane - including the "black boxes," personal effects, and human remains - can be recovered here more easily.
Enough remains are recovered to positively identify everyone on board the plane. Evidence recovered includes knives, passports belonging to the terrorists, and handwritten documents in Arabic describing the terrorists plans for the attack.
Excavation of the crater reaches a depth of 40 feet where aircraft debris is no longer found. On September 24, 2001, the FBI closes its field investigation and the Somerset County Coroner later fills the crater and restores the scene to its condition before September 11.