The government of Venezuela has confirmed the abduction of human rights activist Yon Goicoechea, accusing him of amassing explosive materials on television without confirming the existence of a warrant or evidence against him.

Goicoechea has been an active member of the student movement against socialism since the mid-2000s, organizing campus leaders against late dictator Hugo Chávez. He won the Cato Institute’s 2008 Milton Friedman Prize for Advancing Liberty, whose financial award Venezuelan socialist leaders erroneously referred to as a bribe from the American government.

Goicoechea disappeared early Tuesday morning, with witnesses stating he was forcibly abducted by “armed men.” Later on Tuesday, his wife confirmed the arrest via his Twitter account:

Hello, I am Rosaura, Yon’s wife. At 9:26 AM today, Tuesday 30, I still have not had contact with him or even know where he is. Yon has not been able to speak to his attorneys. We do not know why he was arrested. We fear for his personal safety. Myself and my children want to see Yon free. He is innocent and should be freed immediately.

The Venezuelan Socialist Party (PSUV)’s second-in-command after President Nicolás Maduro, legislative minority leader Diosdado Cabello, confirmed the arrest at a rally Tuesday. Cabello claimed that “in his possession were found detonating cables for explosives.”

“That man was trained by the American empire for years,” Cabello claimed. “It looks like his money ran out and he wants to come here to seek blood. They gave him the order there in the United States.” Goicoechea lived abroad for four years before returning to Venezuela in June. Cabello also warned other opposition activists that they could be next.

American officials have reportedly uncovered significant evidence that Cabello also serves as the head of one of the most lucrative cocaine-smuggling operations in Latin America, the Cartel de los Soles.

The $500,000 in question is the prize money for the Milton Friedman Prize. In a statement on the arrest, the Cato Institute dismissed the charges as lacking “any credibility” and restating that the prize money is coming from a private organization that has nothing to do with the U.S. government. The institute reiterated their praise for Goicoechea for “having led the student movement that played the central role in defeating the constitutional reform that would have given Hugo Chavez what at that time would have been an unprecedented concentration of political and economic power.”

Goicoechea is the latest in a string of prominent opposition leaders to be arrested on suspect charges. The most prominent among these is the head of Goicoechea’s party, Popular Will, the political prisoner Leopoldo López. López was arrested in 2014 on charges of “terrorism” and sentenced to 13 years in prison for inciting violence. López had organized a peaceful protest against Maduro in Caracas. He remains in prison despite the fact that the chief prosecutor in his case has defected to the United States and told reporters he fabricated most of the evidence used to convict López.

Other prominent victims of Maduro’s secret police are the former mayor of Caracas, Antonio Ledezma, and the mayor of western regional capital San Cristóbal, Daniel Ceballos. Journalists who covered the arrest of Ledezma in the capital were also arrested for covering the event.