BEIJING — Late at night, a senior police officer guided Liu Wanyong, then a budding investigative journalist, through the inner sanctum of one of the scariest domains in China, the Ministry of Public Security.

The rooms were empty. Mr. Liu was directed to a locked filing cabinet.

The officer pulled out a dossier, laid the documents on a desk and — this being the era before cellphone cameras — gave Mr. Liu 30 minutes to scratch down the contents.

The documents laid out the story of an innocent businessman who had been jailed for the crimes of a corrupt politician. That’s news in most places, but not of the stop-the-presses variety. But in China in 2005, a leak like that was rare, and Mr. Liu’s account of how a party official had used his power to arrest an innocent man created a sensation.

Eventually, the businessman was released and the politician, a retired Communist Party secretary, went to prison, though not before his supporters attacked Mr. Liu outside the courthouse. For that story, and many others, Mr. Liu earned the nickname “Tibetan Mastiff” for his perseverance at the China Youth Daily, a paper run by the Communist Party but with a reputation for sometimes bending the rules.