On the morning of September 11, 2001, 46 minutes into United Airlines Flight 93, a nonstop flight from Newark, New Jersey to San Francisco, four hijackers took control of the Boeing 757-222. It was around 9:30 a.m., and already that morning, two hijacked planes had shockingly crashed into the World Trade Center in New York City. In less than 10 minutes, another plane would plow into the Pentagon in Washington, D.C.

But what of Flight 93? What is known about its intended target?

What’s known for sure is that at 9:55 a.m., one of its hijackers, Ziad Jarrah, a trained pilot, reset the plane’s autopilot, turning the aircraft around to head back east toward Washington. Already informed about what had happened with the three other hijacked planes through telephone calls with family members, several of the passengers and crew attempted to storm the cockpit occupied by the terrorists. At 10:03 a.m., after a vigorous struggle, the plane crashed in a field near Shanksville, Pennsylvania, killing all 44 people on board. When the plane slammed into the ground at 580 miles per hour, it was about 20 minutes flying time from Washington.

Of the four hijacked planes on September 11, United Airlines Flight 93 was the only one to not reach its intended target. In the most comprehensive study of the terrorists attacks, The 9/11 Commission Report concluded the plane’s target was Washington, where both the Senate and House were in session in the Capitol building. “Jarrah’s objective was to crash his airliner into symbols of the American Republic, the Capitol or the White House,” said the 9/11 report. “He was defeated by the alerted, unarmed passengers of United 93.”

Yet despite the report’s assertions, the ultimate target of Flight 93 remains unknown. Statements made by 9/11 plot conspirators after the attacks offer the strongest clues.

In early 1999, according to the 9/11 report, Khalid Sheikh Mohammed, an al-Qaeda mastermind behind the 9/11 attacks, gained approval from Osama bin Laden to use aircraft as weapons in an attack on the United States. According to Lawrence Wright, author of The Looming Tower: Al-Qaeda and the Road to 9/11, Al Qaeda placed the U.S. on its list of targets in 1998 after it commissioned a study that concluded that Jews controlled the country.

At a meeting in Kandahar, Afghanistan during the spring of 1999, Sheikh Mohammed met with bin Laden and Mohammed Atef, another Al Qaeda leader, to create a list of U.S. targets, which included the White House, the Pentagon, the Capitol and the World Trade Center. These sites stood among America’s most important landmarks—symbols of politics. military and financial power that Al Qaeda wanted to attack.

In 2003, Sheikh Mohammed was arrested during a raid in Pakistan. During his interrogation by U.S. operatives, he said that while bin Ladin wanted to destroy the White House and the Pentagon and to strike the World Trade Center, all his co-conspirators wanted to hit the Capitol. “Everyone agreed on the Capitol…whereas bin Laden favored the Pentagon and White House,” Mohammed said.

Ramzi bin al-Shibh, a Yemeni citizen and conspirator in the plot, is believed by U.S. intelligence officials to be the intended 20th hijacker, but he never received a visa to enter the United States. (Flight 93 had just four terrorists, compared to the other three planes, which had five.) After his arrest in 2002, bin al-Shibh provided interrogators with an organizational structure of the plot, including the thinking of Mohamed Atta, the Egyptian native and plot ringleader who took control of American Airlines Flight 11 and crashed it into the Trade Center’s North Tower. Each terrorist pilot was assigned a location to crash their planes. According to bin al-Shibh, Jarrah, who was on Flight 93, was assigned to the Capitol building in Washington. Atta told bin al-Shibh that if the pilots could not reach their intended targets, they should crash their plane.

Before they were captured and arrested, Sheikh Mohammed and bin al-Shibh told an Al Jazeera reporter that Flight 93 was heading for the Capitol building before passengers attempted to overtake the aircraft.

At 10:15 a.m. on September 11, 2001, officials ordered the Capitol building evacuated. By that time, four hijacked planes had crashed—two into the World Trade Center, one at the Pentagon and one in an empty field in Pennsylvania. In The Only Plane in the Sky: An Oral History of 9/11 by Garrett Graff, then-Republican Speaker of the House Dennis Hastert remembered being whisked away that morning by his security guards. “I said, ‘What’s going on?’ They said, “We think there’s a fourth plane, and we think it’s headed for the Capitol.”

Later that day, some 150 members from the Senate and the House—both Republicans and Democrats—stood on the Capitol steps and sang, “God Bless America.”