Launched in early 2014, the operation was initially thought to be routine - one of a number of similar ongoing probes that the Brazilian Federal Police had on their books.
In this case, the targets were doleiros: black-market money dealers who used small businesses, such as petrol stations and car washes, to launder the profits of crime.
But it soon evolved into one of the biggest and most complex corruption investigations in South American history.
Four years on and Lava Jato - or Operation Car Wash, as it is now known in English - has left its mark on 11 countries, from Brazil to Peru.
Business leaders, multinational corporations and leading politicians have been caught up in allegations ranging from bribery and money laundering to attempting to distort the democratic process, with more than 150 people arrested, prosecuted or facing criminal proceedings.
So how and why did this extraordinary investigation become so far-reaching?
We sent filmmaker Luis del Valle and journalist Gustavo Goritti, from Peru's IDL Reporteros, to find out how prosecutors and police began to unravel a case that has sent shock waves across a continent - and still has some way to run.