Defense Secretary Leon Panetta traveled Tuesday to ground zero in New York — part of a series of Sept 11-related events to mark the 10th anniversary of the terrorist attacks.

Later in the day, he was traveling to Shanksville, Pa., where hijacked United Flight 93 crashed in an open field, killing all 40 passengers and crew members. Nearly 3,000 people were killed that day, including 184 at the Pentagon.

In New York, Panetta planned to tour the National September 11 Memorial, whose two reflecting pools sit within the footprints where the twin towers of the World Trade Center once stood.

In Shanksville, he planned to visit the partially completed Flight 93 Memorial.

Panetta's spokesman, Doug Wilson, said the Pentagon chief wanted to visit Shanksville and New York in order to highlight the role the military has played over the past decade in preventing further attacks on the homeland. Accompanying him on his trip Tuesday were five service members — one each from the Army, Navy, Marine Corps, Air Force and Coast Guard.

The visits also are likely to recall the most memorable event of Panetta's tenure as CIA director: the May killing of al-Qaida leader Osama bin Laden.

Panetta will attend 9/11 memorial events at the Pentagon on Sunday.

Shanksville remains the least publicized of the three 9/11 attack sites. In its final report, the official 9/11 Commission that investigated the terrorist plot wrote a gripping account of what happened aboard Flight 93.

The commission determined that the plane, overtaken by four hijackers, slammed into the ground at 11 seconds past 10:03 EDT, on a path over Pennsylvania toward its intended target in Washington — either the Capitol or the White House.

It departed from Newark, N.J., bound for San Francisco, at 8:42 a.m. The hijackers took over the cockpit 46 minutes later. At 9:57 a.m., a passenger revolt began. The cockpit voice recorder captured sounds of the passenger assault.

"Some family members listening to the recording report that they can hear the voice of a loved one among the din," the 9/11 Commission report said. "We cannot identify whose voices can be heard. But the assault was sustained."

Within minutes, the hijackers apparently determined they were about to be overpowered and decided to abort their mission and destroy the plane.

"The airplane headed down; the control wheel was turned hard to the right. The airplane rolled onto its back, and one of the hijackers began shouting, 'Allah is the greatest. Allah is the greatest.' With the sounds of the passenger counterattack continuing, the aircraft plowed into an empty field in Shanksville, Pa., at 580 mph, about 20 minutes' flying time from Washington, D.C."