CARACAS, Venezuela—The coup plot by disgruntled Venezuelan military officers in March was audacious: Seize control of the capital’s military bases, arrest President Nicolás Maduro and install a provisional government to replace his authoritarian regime.

To avoid detection for a year, conspiring officers eschewed phone calls, texts and emails, and instead sent messages via couriers, said an Army captain who helped plan the thwarted coup. They plotted during seemingly impromptu soccer matches.

Before...