Capital of Brazil until 1960, informally

As a detective, I approach the crossword clue ‘Capital of Brazil until 1960, informally’ with a keen eye for detail and a determination to solve the mystery. First, I note that the clue is referring to the capital of Brazil, so I zone in on the names of cities which have held this title. Then I see that the clue is specifying ‘until 1960’, indicating that the capital changed at some point. After a quick search, I come across the fact that Rio de Janeiro was the capital of Brazil until 1960, when the title was passed on to Brasilia. But the clue is looking for an informal name of the capital, which means I need to dig a little deeper. I find out that the city of Rio de Janeiro is also informally known as ‘RIO’, which fits perfectly with the crossword clue. From my process of elimination and research, I conclude that ‘RIO’ is the answer to the crossword puzzle, and the mystery is solved.