In August 1966 the bodies of two electronics repairmen were found on Vintem Hill in Rio de Janeiro, Brazil. The case became known as the Lead Masks Case.
Miguel Jose Viana and Manoel Pereira da Cruz had left town saying that they were going to buy supplies and a car for their job. On the way, the men stopped at a bar to buy a bottle of water and that was the last time they were to be seen alive.
Three days later, their bodies were found on Vintem Hill. The police were alerted and conducted an investigation. What confused authorities the most was that the men were found wearing suits and waterproof coats, along with lead masks typically used for protection against radiation covering their eyes. There was a water bottle, towels, and a notebook laying near them. In the notebook was a note written in Portuguese that read: “16:30 be at agreed place, 18:30 swallow capsules, after effect protect metals wait for mask signal.”
Theories surrounding the case say that the men were waiting for some sort of extraterrestrial encounter. Others say that the men were duped, murdered, and left on the hill, even though neither man displayed signs of violence. But there were obvious clues. The lead masks suggested they were expecting something radioactive, even though no radioactivity was detected on Vintem Hill. The jackets and towels indicate that there would be moisture.
To this day, no one knows what really happened to the two men. The mystery surrounding who they were meeting, what/where the “arranged place” was, what “protect the metals” really meant, and what these so-called capsules were still remains unsolved.
(Source)