SEOUL, South Korea (AP) — Bereaved relatives of victims of last year’s devastating Halloween crush in Seoul and their supporters demanded an independent investigation of the disaster as they marked the anniversary Sunday with a massive memorial service.

The crush, one of the biggest peacetime disasters in South Korea, killed 159 people, most of them in their 20s and 30s who had gathered in Itaewon, a popular nightlife district in Seoul, for Halloween celebrations.

Commemorating the anniversary, the families visited the Itaewon area, laid flowers and offered condolences at an alley where the crush happened. Some wept near a wall where hosts of post-it notes with condolence messages were plastered.

“I’m sorry. I’m sorry that I couldn’t protect you. I loved you,” Song Jin Young, 55, the father of one of the victims, said.

In Itaewon, accompanied by their supporters, the families also attended multi-faith prayer services for their loved ones. They chanted slogans asking President Yoon Suk Yeol to offer a more sincere apology and Safety Minister Lee Sang-min to resign over the disaster.

“Apologize! Apologize!” they shouted.

The group marched through Seoul before arriving at a square for a memorial service, which drew thousands of people.

In a speech, Lee Jeong-min, a representative for the families, urged President Yoon to support efforts to legislate a special law to open an independent investigation into the disaster.

“We did our utmost to raise our children but we couldn’t even touch them when they vanished all of sudden. Where can we talk about our resentment toward this reality?” Lee said. “The special law would the most important legislation to find the cause of the Itaewon disaster and discuss the prevention of recurrences of similar incidents.”

In speeches, several opposition politicians criticized Yoon for failing to attend the ceremony and vowed to pass the special law to get to the bottom of the tragedy. Some participants reportedly shouted jeers at a ruling party official when he tried to leave after the first half of the ceremony, but there were no reports of major violence.

The memorial ended, with the crowd shouting “We’ll remember you” when names of each of the 159 victims were called. They also placed flowers before the photos of the dead at an altar.

The victims’ families said they had invited Yoon to the memorial ceremony. Instead, he attended a service for the victims at a Seoul church. Yoon’s office didn’t explicitly explain why he missed the memorial, but local media reported it was due to concerns that the event could be used politically by his rivals.

In a speech at the church, Yoon said that the day of the disaster “was the day when I felt the greatest sadness in all my life.” Yoon said he offers deep sympathy to the families and pledged to build a safer South Korea.

In January, a police special investigation concluded that police and municipal officials failed to formulate effective crowd control steps despite correctly anticipating a huge number of people in Itaewon. Investigators said that police had also ignored hotline calls by pedestrians who warned of swelling crowds before the surge turned deadly.

More than 20 police and other officials are reportedly on trial over the disaster. But no top-level officials have been charged or held accountable, a reason why the families and opposition lawmakers call for an independent probe.

This year’s Halloween celebrations in South Korea were largely subdued, with most bars, restaurants and shops avoiding Halloween-themed events in memory of the victims. Only a small number of people dressed in Halloween costumes were seen in Itaewon and other major entertainment zones in Seoul on Friday and Saturday.

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Associated Press video journalist Yong Jun Chang contributed to this report.