In August 1966, two men climbed a remote hill overlooking the Brazilian city of Niterói. They weren't tourists or hikers, but electronics technicians. With them, they carried raincoats, a bottle of water, a slip of paper with brief instructions, and two strange, homemade lead masks.

A few days later, their bodies were found. There were no obvious signs of violence, and investigators couldn't determine what had killed them. But a small note found with the men contained words that turned the case into one of Brazil's most baffling mysteries:

Take the capsule... after the effect... protect metals... wait for the signal... mask.

What was the capsule the men swallowed?

And what was the 'signal' they climbed the hill to wait for?

Why did they believe they needed to protect their eyes with lead masks?

A journey not as their families were told

The two men were Miguel José Viana (34) and Manoel Pereira da Cruz (32), both electronics and television repairmen from Campos dos Goytacazes in the state of Rio de Janeiro.

On August 17, 1966, they left their hometown carrying a large sum of money. According to accounts later given to police, they told others they were going to buy a car and some electronic equipment.

But the men didn't head to their expected destination.

They arrived in Niterói, visited an electronics store, then bought two raincoats and a bottle of mineral water. After that, they made their way to Morro do Vintém hill.

That was the last confirmed sighting of them alive.

Two men lying on the hill

Not long after, two bodies were spotted at the top of the hill. Authorities took some time to reach the site, and by then, decomposition had already set in.

The scene was unusually strange: the men lay side by side, their clothes neat, with no visible fatal injuries. Nearby were their raincoats and some personal belongings. But what would make this case world-famous were the thick, homemade lead masks designed to cover their eyes—without any holes to see through.

A later story claimed the men were found with the masks on their faces, but older sources disagree—some say the masks were next to the bodies or in their hands. So while it's not certain they died wearing the masks, it's clear the lead masks were part of whatever experience brought them to the hill.

The mysterious note

A small note was found in one of the men's clothing, written in Portuguese with brief instructions. The most notable were:

4:30 PM — Arrive at the designated location

6:30 PM — Take the capsule

After the effect... protect the metals... wait for the signal... the mask

The original message was written in a terse style without clear punctuation, which has led to debate over its exact meaning. However, the key words leave little doubt that the two men were following a prearranged plan.

There’s a specific place, a set time, a capsule to be taken, something to do once it takes effect, and finally: wait for a signal. That signal is at the heart of the mystery.

Why lead?

Lead can block or reduce certain types of ionizing radiation, which is why it’s used in medical and nuclear facilities. But a small mask covering only the eyes wouldn’t offer meaningful protection from dangerous radiation. If the men were worried about a bright light, lead wouldn’t be necessary—lighter materials can block visible light. So, the masks seem to reflect the men’s beliefs more than any real threat. They expected something that might emit light, radiation, or some kind of 'energy,' and made protective gear in the way they thought best.

Importantly, the masks didn’t just appear at the scene. Investigators found that the men had been making lead masks in their workshop, along with scraps of metal and related tools. This wasn’t a spontaneous adventure—they had prepared in advance.

Between Electronics and Spirituality

It might seem odd for two electronics technicians to get involved in something like this, but their backgrounds make it more understandable. Investigations and news reports indicate they were interested in spiritual experiments and attempts to contact unknown forces or entities. Their names were also linked to books and ideas that blended spirituality with the concept of life on other planets.

In Brazil at the time, there was a growing movement that combined spirituality, telepathy, extraterrestrials, and mysterious ideas about energy and radiation. It wasn’t unusual for enthusiasts to build devices or conduct their own experiments.

This puts the lead masks in a different light. The men may not have been conducting a scientific experiment in the strict sense, but rather using the language and tools of science to pursue a spiritual belief.

The capsule mattered more than the mask

The case became famous because of the lead masks, but perhaps the most important detail is a single word found in the note: Capsule.

What did the two men swallow at 6:30 p.m.? Was it a drug? A hallucinogen? Some kind of chemical? Poison?

No one knows.

There were also references to taking capsules on other days, suggesting that using some kind of substance wasn’t a spur-of-the-moment decision that night. If the two men ingested something that altered their consciousness, the masks and the 'signal' might have been part of a ritual or experiment aimed at reaching an unusual state of awareness.

But if the capsule was poisonous, the whole mystery might be less about the unknown and more about a tragic chemical accident.

A light on the hill

After news of the bodies spread, a new witness account made the case even stranger. A woman reported seeing a strange object or light near Morro do Vintém hill on the evening of the incident, describing it as glowing blue and orange. The 1960s were a time of global fascination with UFOs, so this testimony quickly became a key part of the 'lead masks' story.

This led to the theory that the two men climbed the hill to wait for a UFO, and that the masks were meant to protect their eyes from its light or radiation.

The problem is that this testimony only surfaced after the story became public, and there’s no physical evidence linking any unidentified object to the men’s deaths. Maybe a light really was seen, but that alone doesn’t tell us what it was or prove it had anything to do with what happened.

Were they tricked by a third person?

There’s another detail that opens up a completely different possibility. The men left home carrying a large sum of money, but most of it was never found with their bodies. This led to the theory that a third person was involved—someone who convinced them he could help them contact a mysterious force, told them to take the capsules as part of a ritual, and then stole their money after they died. In this scenario, the 'spiritual experiment' was just a way to con two men who believed in the supernatural. But there’s no direct evidence for this, and investigators couldn’t link anyone to the deaths.

Was it a suicide attempt?

The idea of a joint suicide was also suggested, but it doesn’t fit easily with the instructions left behind. The note didn’t say 'take the capsule and wait to die'—it described steps, preparations, and a 'signal' that was supposed to come after taking it. Their behavior seems more like people expecting something to happen, not people planning to end their lives. There was also no clear motive for suicide, so while this theory is possible, it’s not the most convincing.

A mistake that may have buried the truth

Forensic science should have solved most of this mystery. If the contents of their stomachs and organs had been analyzed, it might have revealed whether the men took poison, drugs, or hallucinogens. But the condition of the bodies, delays in the investigation, and problems preserving samples meant the best chance for answers was lost. The investigation never reached a clear toxicological conclusion, so the cause of death remains unknown. If the tests had been done properly, we might know what was in the 'capsule'—and the case might never have become a global mystery.

The theory of an experiment gone wrong

When we set aside the legendary embellishments and focus only on the confirmed facts, a relatively simple scenario emerges:

The two men were interested in unusual experiments. They had prepared the lead masks in advance and brought with them instructions specifying the location and time. They were supposed to take a capsule and then wait for a 'signal.' They climbed a remote hill to carry out their plan, and afterward, both died without any obvious signs of violence.

One of the most plausible theories, based on the available evidence, is that the men were conducting a spiritual or pseudo-scientific experiment that ended unexpectedly—possibly due to the substance they ingested. Still, even this theory doesn't answer every question.

Who wrote the instructions?

Did they make the capsule themselves?

What did they expect to happen when the signal arrived?

And why did they believe the lead masks were necessary to protect their eyes?

A mystery born from missing information

The lead masks case is so intriguing because it sits in a gray area between crime, belief, and personal experimentation. There's no evidence that an alien appeared on the hill, nor is there proof that a supernatural force killed the men. But it's also hard to dismiss everything as mere coincidence.

There was a clearly planned ritual, an unknown capsule, specially made masks, and instructions anticipating an event whose nature remains a mystery.

Perhaps the answer was never in the sky at all—maybe it was inside the capsule the men swallowed. With the chance to analyze it lost, we've likely missed the simplest explanation for one of Brazil's strangest twentieth-century mysteries.

And the note's message still lingers, more than half a century later: Wait for the signal.