On August 20, 1966, a boy flying a kite on the Morro do Vintém hill in Niterói, across the bay from Rio de Janeiro, discovered the bodies of two men. The deceased were identified as Manoel Pereira da Cruz and Miguel José Viana, both electronics technicians from Campos. They were dressed in formal suits and raincoats in hot weather, and each wore a crude lead mask — a roughly fashioned eye shield made of lead sheet metal.
A small notebook was found nearby with a cryptic message translating as: "16:30 hours, be at the determined location. 18:30, ingest capsules. After the effect, protect metals, await the signal mask, if no inconvenience." Police found empty water bottles near the bodies. A vendor remembered selling the bottles to the men that day, and also recalled a woman reporting a spacecraft hovering over the hill.
The cause of death was never officially determined — the bodies were decomposed enough that the autopsy was inconclusive, and no capsules or other substances were found. The lead masks, the cryptic note, the formal attire, and the reported aerial phenomenon combine to make the case extraordinary in its strangeness.
The men were known to have an interest in spiritism and prior contact with a group interested in contacting extraterrestrial intelligences. Various theories have been proposed — accidental poisoning from experimental substances ingested in a failed contact protocol, murder, and genuine anomalous event — none definitively established. The Niterói lead masks case remains among the most mysterious and documented unexplained deaths associated with UAP activity.