ANGOLA’S NEW president, João Lourenço, has said one of his highest priorities is to root out the corruption and favoritism that thrived under his predecessor, José Eduardo dos Santos, who ruled for 38 years. Mr. Lourenço should look no farther than the capital city courtroom of Judge Josina Mussua Ferreira Falcão, where he can find a courageous fighter against corruption — in the dock.

Journalist and activist Rafael Marques de Morais has spent nearly two decades uncovering sleazy dealings and official malfeasance. Now he finds himself on trial. His crime? An exposé about a shady land deal published in November 2016 that examined dubious transactions by then-Attorney General João Maria de Sousa and suggested that he was benefiting from protection by Mr. dos Santos. In a recent blog post on his anti-corruption website, Maka Angola, Mr. de Morais recalled his offending language: “The loyalty and support of the President’s appointees is secured by allowing them swill at the same trough.”

His investigation found that the former attorney general, while in office, had significant shares in private companies doing business with the state. Mr. de Morais wrote that the attorney general obtained a title deed for three acres of land, in his private capacity, and planned to build a condo on it. Farmers on the land were evicted. Mr. de Morais reported that it was illegal for the attorney general to be doing such side business while in office. “The whole process was tantamount to corruption,” he says. When he asked for a response to 13 questions on the land issue, he got only silence from the attorney general.

The “answer” soon followed — Mr. de Morais was indicted on Dec. 27, 2016, for defamation and insulting the attorney general. When he provided the evidence he had excavated to support his reporting, the attorney general added charges of violating state security by insulting the president. Each charge carries a maximum penalty of four years in prison. Also being prosecuted is Mariano Brás, editor of the weekly newspaper O Crime, who printed the exposé.

Mr. de Morais has been taking risks to expose corruption for a long time. In 1999, he wrote an article in a small newspaper in which he described Mr. dos Santos as a corrupt dictator. He spent 43 days in prison and has been repeatedly threatened since. He investigated the diamond industry for a book, “Blood Diamonds: Corruption and Torture in Angola.” Last year he was one of five people awarded the Democracy Award from the National Endowment for Democracy.

The charges against Mr. de Morais and Mr. Brás should be dropped immediately. The prosecution is an unsavory legacy of the previous era under Mr. dos Santos, when corruption, nepotism and authoritarianism were rife. If the new president really wants to battle fraud, he should let Mr. de Morais go free, perhaps to teach a new generation of journalists how to hold the powerful to account.

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