CARACAS, Venezuela  News travels fast in this city, and rumors even faster. So when a billionaire banker named Ricardo Fernández Barrueco learned that his home had been searched by agents from the feared secret intelligence police, he might have suspected that the rumors of a purge of magnates loyal to President Hugo Chávez were true.

Being one of Venezuela’s richest and most influential men, Mr. Fernández, 44, went to the headquarters of the Disip intelligence police to clear up the matter directly with the agency’s powerful spymaster.

Then a surprising thing happened, especially in a nation that had grown accustomed to the unfettered activities of pro-Chávez tycoons like Mr. Fernández. The self-described socialist revolution of Mr. Chávez notwithstanding, the prominence of these moguls was so well known it inspired a nickname  the Boligarchs  for their fast accumulation of wealth and their ties to the government, which reveres Simón Bolívar, the 19th-century aristocrat who won Venezuela’s freedom from Spain.

But instead of dismissing the matter, the intelligence chief imprisoned Mr. Fernández last year and ordered agents to start detaining other pro-Chávez magnates. Some slipped into hiding abroad and are still being sought. Several others and their associates were arrested and put in cells adjacent to Mr. Fernández’s.