Many loved ones of the nearly 3,000 people killed were joining dignitaries and politicians at commemorations Thursday in New York, at the Pentagon and in Shanksville, Pennsylvania.

On Thursday morning, Denise Matuza, Jennifer Nilsen and Michelle Pizzo boarded a bus from Staten Island for Lower Manhattan — each wearing T-shirts emblazoned with the names and faces of their husbands, who died in the attack.

“Even 24 years later, it’s heart wrenching,” said Nilsen, whose husband, Troy Nilsen, worked at Cantor Fitzgerald on the 103rd floor of the World Trade Center. “It feels the same way every year.”

For Ronald Bucca, who lost his father, the FDNY fire marshal Ronald Paul Bucca, the annual memorial served as an opportunity to “educate people on that day, especially the younger generations, and learn from each other how to be resilient and deal with loss and rebuild.”

Pizzo, whose husband, Jason DeFazio, also worked at Cantor Fitzgerald, hoped more people could just take one minute to reflect on the day.

“Younger kids don’t realize that you have to remember,” she said.

The remembrances are being held during a time of increased political tensions. The 9/11 anniversary, often promoted as a day of national unity, comes a day after conservative activist Charlie Kirk was shot and killed while speaking at a college in Utah.

The reading of names and moments of silence

Kirk’s killing prompted additional security measures around the 9/11 anniversary ceremony at the World Trade Center site in New York.

Vice President JD Vance and his wife, second lady Usha Vance, had planned to attend the event in Manhattan but instead are set to visit with Kirk’s family on Thursday in Salt Lake City, according to a person familiar with Vance’s plans, but not authorized to speak about them publicly.

Many in the crowd at Thursday’s ceremony at ground zero held up photos of lost loved ones as a moment of silence marked the exact time when the first hijacked plane struck the World Trade Center’s iconic twin towers. Family members then began reading aloud the names of the victims.

At the Pentagon in Virginia, the 184 service members and civilians killed when hijackers steered a jetliner into the headquarters of the U.S. military were being honored in a ceremony attended by President Donald Trump and first lady Melania Trump. The president was then expected to head to the Bronx for a baseball game between the New York Yankees and Detroit Tigers Thursday evening.

And in a rural field near Shanksville, Pennsylvania, a similar ceremony marked by moments of silence, the reading of names and the laying of wreaths, will honor the victims of Flight 93, the hijacked plane that crashed after crew members and passengers tried to storm the cockpit. That service will be attended by Veterans Affairs Secretary Doug Collins.

People across the country are also marking the 9/11 anniversary with service projects and charity works as part of a national day of service. Volunteers will be taking part in food and clothing drives, park and neighborhood cleanups, blood banks and other community events.

Reverberations from attacks persist

In all, the attacks by al-Qaida militants killed 2,977 people, including many financial workers at the World Trade Center and firefighters and police officers who had rushed to the burning buildings trying to save lives.

The attacks reverberated globally and altered the course of U.S. policy, both domestically and overseas. It led to the “ Global War on Terrorism ” and the U.S.-led invasions of Afghanistan and Iraq and related conflicts that killed hundreds of thousands of troops and civilians.

While the hijackers died in the attacks, the U.S. government has struggled to conclude its long-running legal case against the man accused of masterminding the plot, Khalid Sheikh Mohammed. The former al-Qaida leader was arrested in Pakistan in 2003 and later taken to a U.S. military base at Guantánamo Bay, Cuba, but has never received a trial.

The anniversary ceremony in New York was taking place at the National Sept. 11 memorial and Museum, where two memorial pools ringed by waterfalls and parapets inscribed with the names of the dead mark the spots where the twin towers once stood.

The Trump administration has been contemplating ways that the federal government might take control of the memorial plaza and its underground museum, which are now run by a public charity currently chaired by former New York City Mayor Michael Bloomberg, a frequent Trump critic. Trump has spoken of possibly making the site a national monument.

In the years since the attacks, the U.S. government has spent billions of dollars providing health care and compensation to tens of thousands of people who were exposed to the toxic dust that billowed over parts of Manhattan when the twin towers collapsed. More than 140,000 people are still enrolled in monitoring programs intended to identify those with health conditions that could potentially be linked to hazardous materials in the soot.

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Associated Press reporters Jake Offenhartz and Liseberth Guillaume in New York City, Michael Hill in Albany, New York, and Michelle L. Price and Darlene Superville in Washington contributed to this story.