Roberto Samcam Ruiz took security measures seriously.

A retired Nicaraguan Army major who had spoken out against the Sandinista government, he fled to neighboring Costa Rica after his name started popping up on wanted posters.

When out in public in San José, the Costa Rican capital, he changed shirts to throw off any would-be followers. He rode in Ubers — never buses — and constantly warned other Nicaraguan anti-government activists living in Costa Rica to watch their backs.

“At one point, he became totally paranoid,” said Claudia Vargas, his wife of 25 years.

Mr. Samcam’s precautions were not enough.

On June 19, two assassins who had apparently staked him out for weeks stormed his condominium complex in San José and shot him eight times inside his home.

Mr. Samcam’s killing became at least the sixth time a Nicaraguan dissident was shot, abducted or killed in Costa Rica since hundreds of thousands of Nicaraguans fled their country after deadly protests there in 2018.