RIO DE JANEIRO — The heist was cinematically daring even for the South American borderland famed as a smuggler’s haven.

In the dead of night, the squad of outlaws set cars ablaze on the streets of Ciudad del Este, the Paraguayan city on the so-called Triple Frontier where Paraguay, Brazil and Argentina share a border. Amid the chaos, they sprayed gunfire on the entrance of a Spanish cash transporting company before using explosives to blast their way into the safe room.

After the crew stole millions of dollars in cash and fatally shot a police officer at the scene on Monday, some of the assailants fled by boat across the vast reservoir of the Itaipu Dam to Brazil. Security forces on Brazilian soil engaged them in a gun battle, killing three of the suspects and arresting at least eight others.

“This is something war-torn countries endure,” said Cornelio Melgarejo, the director of a shelter for street children adjacent to the plundered complex in Ciudad del Este. Still, he added, “It’s not every day you hear the blast of explosives in a place where children are sleeping.”