LISBON (AP) — Ana Lopes worked at a Catholic charity in Portugal ‘s capital, often commuting up and down a hill on one of Lisbon’s famed yellow-and-white streetcars.

The 50-something woman helped dozens of people navigate the adoption of children, a trying process that can take a decade. Her benevolent work came to a an abrupt end Wednesday when her streetcar careened off its tracks and crashed into a building.

“It’s a huge tragedy. It’s very difficult to understand what’s happening to us,” Gonçalo de Oliveira, 44, said through tears on Friday. Lopes had shepherded him and his partner through an adoption that had been a lifelong dream, and he often met up with her at family reunions and events.

“There was no apparent risk, yet, all of a sudden, it just happened. We lost 16 lives, Portuguese, foreigners, it doesn’t matter. Lives.”

De Oliveira was among around 100 people who gathered at Lisbon’s Church of Saint Roch on Friday to mourn the victims. In addition to Lopes, three other Portuguese nationals who worked at the Santa Casa da Misericordia charity died.

Co-worker Jose Freire had known one of the victims for over three decades.

“It’s very difficult, very sad,” he said outside on the church steps. He recalled that many of his colleagues regularly took the Elevador da Gloria streetcar, and said that he wanted Portuguese officials to figure out what happened quickly and fix it so that it never happens again.

Multiple agencies are investigating what Prime Minister Luis Montenegro has described as “one of the biggest tragedies of our recent past.”

Officials have not yet said what caused the accident.

The distinctive streetcar, which is classified as a national monument, was packed with locals and international tourists on Wednesday evening when it came off its rails.

Retiree Maria das Neves, who used to work at Santa Casa da Misericordia, is also grieving the loss of her former colleagues.

“There is a fraternity among those who work in this house. We are like a family,” she said as she descended the church’s steps. “I felt love and friendship toward them and I will always feel close to them.”