Over the last 10 years, Robert Mugabe’s government has destroyed Zimbabwe’s economy and eviscerated freedom in the country. In addition to the many victims of state-sponsored violence, hundreds of thousands of people died as a result of avoidable hunger and sickness.

Yet most African leaders either passively watched or actively supported the criminal regime in Harare. A trial that will start today in Kenya may show that the U.N. has also betrayed the people of Zimbabwe by cozying up to the dictator and hiding the truth about one of the worst episodes in that African country.

Georges Tadonki, who heads the U.N. Office for the Coordination of Humanitarian Affairs (OCHA) in Harare, alleges that the top U.N. official in Zimbabwe at the time knowingly ignored the 2008 cholera outbreak in the country. By the time the U.N. finally intervened in late December 2008, Mr. Tadonki told the press, there were already “over 4,000 deaths, more than 100,000 people sick of cholera and millions [of] people affected directly or indirectly not only in Zimbabwe, but also in neighboring South Africa, Zambia, and Mozambique.”

According to Roger Bate of the American Enterprise Institute, “the mortality rate was at least four times, maybe five times, higher than one would expect—even allowing for the parlous state of the Zimbabwean health-care system. The mortality rate was similar to the outbreaks before the discovery of the transmission process in mid-19th century.”

The crisis started when the Mugabe government nationalized Zimbabwe’s water supply in 2005 but soon ran out of money to maintain the infrastructure and treat the water with sodium sulfate. In 2008 the government shut down the water supply altogether, reducing the people in the urban areas to scavenge for water in ponds and sewers. Since the Zimbabwean health-care system collapsed along with the rest of the economy, the U.N. effectively became responsible for providing the necessary aid to tackle the emerging health crisis.

However, Mr. Tadonki says that Agostinho Zacarias, who headed the overall U.N. mission in Zimbabwe at the time and was since promoted to another U.N. position, refused to give the go-ahead for anti-cholera measures even though Mr. Tadonki and his staff advised him that an outbreak of the disease was very likely. Moreover, Mr. Tadonki says, the U.N. made only minimal efforts to galvanize the international assistance needed to arrest the spread of the disease between its outbreak in August 2008 and early December 2008. Those four months were crucial because cholera is highly contagious, has an incubation period between one and two days and can kill soon afterwards.

Mr. Tadonki claims that the U.N.‘s refusal to rapidly move on cholera was not simple negligence but politically motivated. According to Mr. Tadonki, the U.N. didn’t want to anger the host government, which was trying to convince the world in general and Africa in particular that all was well in Zimbabwe. The government’s official line—spelled out by Mugabe as late as December 2008—was that there was “no cholera.” According to Mr. Tadonki, his former superior, Mr. Zacarias, aligned the U.N. “behind a humanitarian situation analysis ‘acceptable’ to [the] government.”

The U.N. rewarded Mr. Tadonki’s criticism with a threat of dismissal, which prompted him to sue the U.N. for harassment at the U.N. Dispute Tribunal in Nairobi, Kenya. International lawyer Robert Amsterdam, famous for defending the Russian political prisoner Mikhail Khodorkovsky, is Mr. Tadonki’s pro-bono legal counsel.

Did the UN fail to fulfill its mission to protect the people of Zimbabwe out of political considerations? Did it make matters worse by refusing to acknowledge the outbreak of the epidemic? Those are some of the questions that the trial may soon answer.