To gather evidence, the competition authorities create a "prisoners' dilemma", by offering leniency to any cartel member willing to provide evidence against his or her co-conspirators. In India, it appears that the leniency program lead to evidence of price fixing:
The CCI was tipped off by one of the three companies after it filed a leniency application with the regulator, revealing details of the alleged price fixing, he added.
The regulator’s leniency program is a type of whistleblower protection offered to cartel members.
The government source said that the raids found email exchanges showing that the companies were fixing prices. “That is smoking gun evidence,” the source said.HT: Matt B.