U.S. President Joe Biden and first lady Jill Biden depart after visiting the nearby site in Shanksville where the hijacked United Airlines Flight 93 plane crashed, on the 20th anniversary of the September 11, 2001 attacks, the Pennsylvania Army National Guard Base in Johnstown, Pennsylvania, U.S., September 11, 2021. REUTERS/Jonathan Ernst 

U.S. first lady Jill Biden brings beer as she and President Joe Biden arrive to greet people at the Shanksville volunteer fire station, stopping at the fire hall after visiting the nearby site where the hijacked United Airlines Flight 93 plane crashed, on the 20th anniversary of the September 11, 2001 attacks, in Shanksville, Pennsylvania, U.S., September 11, 2021. Biden has repeatedly visited the firehouse over the years since 2001. REUTERS/Jonathan Ernst 

U.S. President Joe Biden speaks to reporters before paying his respects at a 9/11 memorial outside the Shanksville volunteer fire station, as he and first lady Jill Biden stopped at the fire hall after visiting the nearby site where the hijacked United Airlines Flight 93 plane crashed, on the 20th anniversary of the September 11, 2001 attacks, in Shanksville, Pennsylvania, U.S., September 11, 2021. Biden has repeatedly visited the firehouse over the years since 2001. REUTERS/Jonathan Ernst 

U.S. President Joe Biden pays his respects at a 9/11 memorial outside the Shanksville volunteer fire station, as he and first lady Jill Biden stopped at the fire hall after visiting the nearby site where the hijacked United Airlines Flight 93 plane crashed, on the 20th anniversary of the September 11, 2001 attacks, in Shanksville, Pennsylvania, U.S., September 11, 2021. Biden has repeatedly visited the firehouse over the years since 2001. REUTERS/Jonathan Ernst 

U.S. President Joe Biden hugs a woman while visiting firefighters outside the Shanksville volunteer fire station, as he and first lady Jill Biden stopped at the fire hall after visiting the nearby site where the hijacked United Airlines Flight 93 plane crashed on the 20th anniversary of the September 11, 2001 attacks, in Shanksville, Pennsylvania, U.S., September 11, 2021. Biden has repeatedly visited the firehouse over the years since 2001. REUTERS/Jonathan Ernst 

United Airlines flight attendants who fly the Flight 93 route watch and listen as U.S. President Joe Biden talks to reporters outside the Shanksville volunteer fire station, as he and first lady Jill Biden stopped at the fire hall after visiting the nearby site where the hijacked United Airlines Flight 93 plane crashed on the 20th anniversary of the September 11, 2001 attacks, in Shanksville, Pennsylvania, U.S., September 11, 2021. Biden has repeatedly visited the firehouse over the years since 2001. REUTERS/Jonathan Ernst 

U.S. President Joe Biden greets firefighters outside the Shanksville volunteer fire station, as he and first lady Jill Biden stopped at the fire hall after visiting the nearby site where the hijacked United Airlines Flight 93 plane crashed on the 20th anniversary of the September 11, 2001 attacks, in Shanksville, Pennsylvania, U.S., September 11, 2021. Biden has repeatedly visited the firehouse over the years since 2001. REUTERS/Jonathan Ernst 

U.S. President Joe Biden pays his respects at a 9/11 memorial outside the Shanksville volunteer fire station, as he and first lady Jill Biden stopped at the fire hall after visiting the nearby site where the hijacked United Airlines Flight 93 plane crashed, on the 20th anniversary of the September 11, 2001 attacks, in Shanksville, Pennsylvania, U.S., September 11, 2021. Biden has repeatedly visited the firehouse over the years since 2001. REUTERS/Jonathan Ernst 

U.S. President Joe Biden pays his respects at a 9/11 memorial outside the Shanksville volunteer fire station, as he and first lady Jill Biden stopped at the fire hall after visiting the nearby site where the hijacked United Airlines Flight 93 plane crashed, on the 20th anniversary of the September 11, 2001 attacks, in Shanksville, Pennsylvania, U.S., September 11, 2021. Biden has repeatedly visited the firehouse over the years since 2001. REUTERS/Jonathan Ernst 

U.S. President Joe Biden talks with reporters outside the Shanksville volunteer fire station, as he and first lady Jill Biden stopped at the fire hall after visiting the nearby site where the hijacked United Airlines Flight 93 plane crashed, on the 20th anniversary of the September 11, 2001 attacks, in Shanksville, Pennsylvania, U.S., September 11, 2021. Biden has repeatedly visited the firehouse over the years since 2001. REUTERS/Jonathan Ernst 

U.S. President Joe Biden talks with reporters outside the Shanksville volunteer fire station, as he and first lady Jill Biden stopped at the fire hall, after visiting the nearby site where the hijacked United Airlines Flight 93 plane crashed, on the 20th anniversary of the September 11, 2001 attacks, in Shanksville, Pennsylvania, U.S., September 11, 2021. Biden has repeatedly visited the firehouse over the years since 2001. REUTERS/Jonathan Ernst 

U.S. President Joe Biden talks with reporters outside the Shanksville volunteer fire station, as he and first lady Jill Biden stopped at the fire hall after visiting the nearby site where the hijacked United Airlines Flight 93 plane crashed on the 20th anniversary of the September 11, 2001 attacks, in Shanksville, Pennsylvania, U.S., September 11, 2021. Biden has repeatedly visited the firehouse over the years since 2001. REUTERS/Jonathan Ernst 

Paramedic Christian Boyd, one of the first responders on 9/11, rings a bell of remembrance for each person who died on the hijacked United Airlines Flight 93 plane crash, during an event commemorating the 20th anniversary of the September 11, 2001 attacks at the Flight 93 National Memorial in Stoystown, Pennsylvania, U.S., September 11, 2021. REUTERS/Evelyn Hockstein 

U.S. President Joe Biden talks with a woman while visiting firefighters outside the Shanksville volunteer fire station, as he and first lady Jill Biden stopped at the fire hall after visiting the nearby site where the hijacked United Airlines Flight 93 plane crashed on the 20th anniversary of the September 11, 2001 attacks, in Shanksville, Pennsylvania, U.S., September 11, 2021. Biden has repeatedly visited the firehouse over the years since 2001. REUTERS/Jonathan Ernst 

U.S. President Joe Biden hugs a woman while visiting firefighters outside the Shanksville volunteer fire station, as he and first lady Jill Biden stopped at the fire hall after visiting the nearby site where the hijacked United Airlines Flight 93 plane crashed on the 20th anniversary of the September 11, 2001 attacks, in Shanksville, Pennsylvania, U.S., September 11, 2021. Biden has repeatedly visited the firehouse over the years since 2001. REUTERS/Jonathan Ernst 

U.S. first lady Jill Biden hands out six packs of beers to firefighters outside the Shanksville volunteer fire station, as she and President Joe Biden stopped at the fire hall after visiting the nearby site where the hijacked United Airlines Flight 93 plane crashed on the 20th anniversary of the September 11, 2001 attacks, in Shanksville, Pennsylvania, U.S., September 11, 2021. Biden has repeatedly taken the firefighters at the station beers and food over the years since 2001. REUTERS/Jonathan Ernst 

U.S. President Joe Biden and first lady Jill Biden greet firefighters outside the Shanksville volunteer fire station, as Biden stopped at the fire hall after visiting the nearby site where the hijacked United Airlines Flight 93 plane crashed on the 20th anniversary of the September 11, 2001 attacks, in Shanksville, Pennsylvania, U.S., September 11, 2021. REUTERS/Jonathan Ernst 

U.S. President Joe Biden and first lady Jill Biden greet firefighters outside the Shanksville volunteer fire station, as Biden stopped at the fire hall after visiting the nearby site where the hijacked United Airlines Flight 93 plane crashed on the 20th anniversary of the September 11, 2001 attacks, in Shanksville, Pennsylvania, U.S., September 11, 2021. REUTERS/Jonathan Ernst 

U.S. President Joe Biden, first lady Jill Biden, and others join families of loved ones in a walk to the boulder which marks the general location of the impact site where the hijacked United Airlines Flight 93 plane crashed, on the 20th anniversary of the September 11, 2001 attacks, in Stoystown, Pennsylvania, U.S., September 11, 2021. REUTERS/Hannah Beier 

People watch as U.S. Vice President Kamala Harris stands next to the boulder which marks the general location of the impact site where the hijacked United Airlines Flight 93 plane crashed during an event commemorating the 20th anniversary of the September 11, 2001 attacks, in Stoystown, Pennsylvania, U.S., September 11, 2021. REUTERS/Hannah Beier 

People walk to the boulder which marks the general location of the impact site where the hijacked United Airlines Flight 93 plane crashed during an event commemorating the 20th anniversary of the September 11, 2001 attacks, in Stoystown, Pennsylvania, U.S., September 11, 2021. REUTERS/Hannah Beier 

U.S. Vice President Kamala Harris walks to the boulder which marks the general location of the impact site where the hijacked United Airlines Flight 93 plane crashed during an event commemorating the 20th anniversary of the September 11, 2001 attacks, in Stoystown, Pennsylvania, U.S., September 11, 2021. REUTERS/Hannah Beier 

The boulder which marks the general location of the impact site where the hijacked United Airlines Flight 93 plane crashed is pictured at the base of the hemlock grove at the Flight 93 National Memorial near Shanksville, Pennsylvania, U.S., September 11, 2021. This photo was taken at 8.46am EDT on September 11, 2021, exactly 20 years after the first plane struck the North Tower of the World Trade Center in New York. REUTERS/Hannah Beier 

People join U.S. Vice President Kamala Harris (3d L) as she walks towards the boulder which marks the general location of the impact site where the hijacked United Airlines Flight 93 plane crashed during an event commemorating the 20th anniversary of the September 11, 2001 attacks, at the Flight 93 National Memorial in Stoystown, Pennsylvania, U.S., September 11, 2021. REUTERS/Evelyn Hockstein 

People walk towards the boulder which marks the general location of the impact site where the hijacked United Airlines Flight 93 plane crashed during an event commemorating the 20th anniversary of the September 11, 2001 attacks at the Flight 93 National Memorial in Stoystown, Pennsylvania, U.S., September 11, 2021. REUTERS/Evelyn Hockstein 

U.S. Vice President Kamala Harris (2nd L) walks with other officials towards the boulder which marks the general location of the impact site where the hijacked United Airlines Flight 93 plane crashed during an event commemorating the 20th anniversary of the September 11, 2001 attacks at the Flight 93 National Memorial in Stoystown, Pennsylvania, U.S., September 11, 2021. REUTERS/Evelyn Hockstein 

The boulder which marks the general location of the impact site where the hijacked United Airlines Flight 93 plane crashed is pictured at the base of the hemlock grove at the Flight 93 National Memorial near Shanksville, in Stoystown, Pennsylvania, U.S., September 2, 2021. Picture taken September 2, 2021. REUTERS/Hannah Beier 

Arborist Ben Haupt, who worked to recover the debris from the hijacked United Airlines Flight 93 near Shanksville, looks out at the flight path where the plane crashed in Stoystown, Pennsylvania, U.S., September 2, 2021. Picture taken September 2, 2021. REUTERS/Hannah Beier 

Passengers from plane that was hijacked and diverted to Malta return to Tripoli's Mitiga International Airport, Libya, December 24, 2016. REUTERS/Hani Amara 

Passengers from plane that was hijacked and diverted to Malta return to Tripoli's Mitiga International Airport, Libya, December 24, 2016. REUTERS/Hani Amara 

Passengers (C) from plane that was hijacked and diverted to Malta return to Tripoli's Mitiga International Airport, Libya, December 24, 2016. REUTERS/Hani Amara 

Passengers from plane that was hijacked and diverted to Malta return to Tripoli's Mitiga International Airport, Libya, December 24, 2016. REUTERS/Hani Amara TPX IMAGES OF THE DAY 

Passengers from plane that was hijacked and diverted to Malta return to Tripoli's Mitiga International Airport, Libya December 24, 2016. REUTERS/Hani Amara 

One of the hijackers of a Libyan Afriqiyah Airways Airbus A320 surrenders to Maltese military on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zammit-Lupi MALTA OUT 

Two hijackers of a Libyan Afriqiyah Airways Airbus A320 surrender to Maltese military on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zammit-Lupi MALTA OUT 

Two hijackers of a Libyan Afriqiyah Airways Airbus A320 surrender to Maltese military on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zammit-Lupi MALTA OUT 

Two hijackers of a Libyan Afriqiyah Airways Airbus A320 surrender to Maltese military on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zammit-Lupi MALTA OUT 

One of the hijackers of a Libyan Afriqiyah Airways Airbus A320 waves a Gaddafi-era Libyan flag at Malta Airport, December 23, 2016. REUTERS/Darrin Zammit-Lupi MALTA OUT 

Two hijackers of a Libyan Afriqiyah Airways Airbus A320 surrender to Maltese military on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zammit-Lupi MALTA OUT 

Two hijackers of a Libyan Afriqiyah Airways Airbus A320 surrender to Maltese military on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zammit-Lupi MALTA OUT 

Two hijackers of a Libyan Afriqiyah Airways Airbus A320 surrender to Maltese military on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zammit-Lupi MALTA OUT 

Two hijackers of a Libyan Afriqiyah Airways Airbus A320 surrender to Maltese military on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zammit-Lupi MALTA OUT 

Two hijackers of a Libyan Afriqiyah Airways Airbus A320 surrender to Maltese military on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zammit-Lupi MALTA OUT 

People disembark from a hijacked Libyan Afriqiyah Airways Airbus A320 on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zammit-Lupi MALTA OUT 

People disembark from a hijacked Libyan Afriqiyah Airways Airbus A320 on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zammit-Lupi MALTA OUT 

People disembark from a hijacked Libyan Afriqiyah Airways Airbus A320 on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zammit-Lupi MALTA OUT 

People disembark from a hijacked Libyan Afriqiyah Airways Airbus A320 on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zammit-Lupi MALTA OUT 

Two airliners pass in the sky above Malta as the drama of a hijacked Libyan Afriqiyah Airways Airbus A320 is played out on the runway beneath at Malta Airport, December 23, 2016. REUTERS/Darrin Zammit-Lupi MALTA OUT 

People disembark from a hijacked Libyan Afriqiyah Airways Airbus A320 on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zamit-Lupi MALTA OUT 

People disembark from a hijacked Libyan Afriqiyah Airways Airbus A320 on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zamit-Lupi MALTA OUT 

People disembark from a hijacked Libyan Afriqiyah Airways Airbus A320 on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zamit-Lupi MALTA OUT 

People disembark from a hijacked Libyan Afriqiyah Airways Airbus A320 on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zamit-Lupi MALTA OUT 

Maltese troops survey a hijacked Libyan Afriqiyah Airways Airbus A320 on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zammit-Lupi MALTA OUT 

A hijacked Libyan Afriqiyah Airways Airbus A320 stands on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zammit-Lupi MALTA OUT 

A hijacked Libyan Afriqiyah Airways Airbus A320 stands on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zammit-Lupi MALTA OUT 

A Maltese military vehicle stands near a hijacked Libyan Afriqiyah Airways Airbus A320 on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zamit-Lupi MALTA OUT 

A Maltese military vehicle stands near a hijacked Libyan Afriqiyah Airways Airbus A320 on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zamit-Lupi MALTA OUT 

Maltese troops survey a hijacked Libyan Afriqiyah Airways Airbus A320 on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zamit-Lupi MALTA OUT 

Maltese troops survey a hijacked Libyan Afriqiyah Airways Airbus A320 on the runway at Malta Airport, December 23, 2016. REUTERS/Darrin Zamit-Lupi MALTA OUT