“We didn’t even have money for toilet paper,” said Mr. de Souza, the anthropologist, who has worked at the museum for 38 years.

There were a handful of missed opportunities that could have enabled museum personnel to take better care of the building and its contents.

University officials and the World Bank discussed the possibility of securing a loan in the 1990s, but the talks fizzled. In 2014, the federal government approved an $8.6 million package to modernize the museum. But the money ultimately was not disbursed.

In recent years, the museum turned to Brazil’s National Development Bank for help. After a protracted negotiation, the bank this year committed to funding a series of improvements worth $5 million, which would have included a fire suppression system.

The overhauls were due to start late this year.

After the fire, Daniela Alarcon, an anthropologist at the National Museum who studies the Tupinambá people from the northeastern state of Bahia, collected statements about its loss from leaders from the tribe.

“That place was like a memory, a computer hard drive, that at any moment, any ethnic group, from any people, could access to get information, to know where they were, to not feel lost,” one of those leaders, Glicéria Jesus Silva, told Ms. Alarcon.

To her, the building felt like a homecoming.

“You came from here, this is your origin,” she said, describing what the museum meant to her. “What was there won’t ever come back, no one can replace it.”