Hopes for dozens of students feared trapped in rubble at a collapsed boarding school have turned to anguish as authorities shift their focus from rescue to recovery.

Suharyanto, the head of Indonesia’s National Disaster Management Agency, told a news conference on Thursday that thermal drones and other equipment had found “no additional signs of life” at Al-Khoziny Islamic Boarding School.

Relatives of the missing students collapsed in the streets around the site and wailed in anguish upon hearing the news.

Authorities said they would bring in heavy machinery to assist in recovery efforts.

Until now, they had resisted bringing in excavators to clear the debris for fear of harming anyone trapped alive.

Authorities have sealed off the school, which officials say collapsed as construction workers were laying concrete on the building’s fourth floor, as rescuers continue to painstakingly pick through the debris for the 59 people believed missing.

But even hundreds of metres from the scene, the smell of decomposing bodies was overwhelming.

The missing are “all dead”, said a junior police officer standing guard at the scene, asking not to be named. He said it had long been suspected that most of the students trapped inside the school had perished.

Family members who have been sleeping at the scene since Monday, when the building collapsed, lined up at an on-site tent on Thursday to give DNA samples in the hopes of identifying their loved ones.

Ahmad Ichsan, whose 14-year-old son Arif Affandi is believed to be trapped, wiped away tears and murmured a prayer as doctors from the neighbouring city of Surabaya prepared to take a buccal swab.

“He has been at the boarding school for two years and four months,” Ichsan, who is from Madura, an island about 33km northeast of Sidoarjo, told Al Jazeera.

“I sent him to school here so that he would learn to be a good son and be devoted to his parents and devoted to his country.” Ichsan said he found out about the collapse from the parent of another child in his son’s class. “I immediately came to the school. I have been here ever since,” he said. “They haven’t found him yet, but I still have hope he is alive.”

Late on Wednesday evening, five students were found alive in an air pocket of the collapsed building, fuelling hopes that more could be saved.

Those hopes seemed increasingly fragile on Thursday as the “golden window” – the critical 72-hour period cited by experts as crucial for finding disaster victims alive – expired.

Five students have been confirmed dead so far, and more than 100 people were injured.

Muhammad Sobir said he was holding out hope that his 13-year-old son, Nurdin, would be found alive.

“God willing, he will be found alive. I will stay here until they find him,” he told Al Jazeera.

Nurdin, from neighbouring Madura, had only been at the school for four months, Sobir said.

“We chose this boarding school as it is known for providing a high-quality education. Nurdin is a good boy, such a good boy, and so diligent in his studies,” he said.

Sobir said he did not know what had caused the school to collapse, but that it was not his primary focus.

“I don’t know what happened, but I can’t think about that at the moment,” he said.

“I saw what happened on television. I was actually watching it on the news at the time, and I rushed here, but no one has seen my boy.”

Sobir’s wife, Nur Fatria, also gave a buccal swab to the forensic team. “I can’t even tell you what I feel having to do this test,” she told Al Jazeera. “I’m still in shock and confused. I don’t know what I feel any more. I have been here for four days.”

Deris, a forensic police doctor, said both parents of those missing are being asked to provide DNA samples so they can be cross-referenced.

[Aljazeera]