Even government officials have been vocal in their support of Mr. Campiani and his partners.

“Leadgate has very bad press, but their management was a management that increased destinations, reduced liabilities, increased the number of passengers, and improved the positioning of the airline in the region,” the country’s minister of transport, Victor Rossi, said in a 2012 interview with El Observador, a newspaper in Montevideo.

He later reiterated this view, saying, “I would have never shut down Pluna.”

Other factors worked against Leadgate. The populist government of Mr. Mujica mistrusted the partners of a private equity firm.

“So far we have always lost with the capitalists,” the then president said. About the Leadgate partners, he said, “It is difficult to get a grip on them because they are slippery like eels.”

In March, Mr. Vázquez was again elected president and his moderate faction returned to power.

Despite the exit of Mr. Mujica, Mr. Campiani remains incarcerated, as his colleagues were, because of the peculiarities of the Uruguayan judicial system. Uruguay is one of only a few democracies in the world where citizens can be legally held without charges for years at a time.

Since the Leadgate partners were imprisoned, the government has continued to take testimony from witnesses, trying to build its case against Mr. Campiani and his colleagues. But of the 41 witnesses called so far — including President Vázquez and top government officials — none have described any illegal activity by the three men.