Shortly after 3 a.m., a battering ram burst open the door to a 14th-floor apartment and three men dressed in the black tactical gear of the Chilean police rushed in. Brandishing guns, they grabbed Ronald Ojeda in front of his wife and 6-year-old son and dragged him away in his underwear.

Mr. Ojeda, a 32-year-old former Venezuelan Army officer, was a political dissident living under asylum in a middle-class neighborhood of Chile’s capital, Santiago. He had tried to organize plots to topple Nicolás Maduro, Venezuela’s autocratic leader, and weeks earlier, Mr. Maduro's government had publicly labeled him a traitor.

When his wife called the Chilean authorities, she told them that at least one of her husband’s captors had a Venezuelan accent.

Across town nine days later, the authorities, acting on a tip, discovered a carry-on suitcase buried under nearly five feet of concrete. Inside, packed amid quicklime to speed up the decomposition, was Mr. Ojeda’s folded body.

Now, after a year of investigation, Chilean authorities are confirming the fears of Venezuelan dissidents hiding out around the world: The evidence, the Chileans said, indicates that Mr. Maduro’s government ordered Mr. Ojeda’s assassination.

The Maduro government has vehemently denied that.

If true, the case represents a dark escalation in Mr. Maduro’s efforts to crush any threats to his authoritarian rule — and the accusations arrive just as President Trump opens a new dialogue with the autocrat in hopes of deporting undocumented Venezuelans.