In 1966, two Brazilian technicians were discovered dead on Vintém Hill in Rio de Janeiro. They wore formal suits, raincoats, and crude lead eye masks. A nearby notebook contained cryptic instructions about ingesting capsules and awaiting a "mask signal". Due to delayed autopsies, their cause of death was never determined. This bizarre, unsolved mystery has sparked enduring theories involving UFO cults, accidental drug overdoses, and foul play.