In 1961, Soviet cosmonaut Yuri Gagarin made history as the first person to leave Earth and enter outer space. However, according to two Italian brothers who claimed they began monitoring Soviet Space program transmissions in 1957, there were others that went before him – but didn't make it back alive.

The Soviet Space program, like the US space program, has not been without its disasters. Unsurprisingly, launching people to space less than a century after seconds-long flights on Earth were considered revolutionary was incredibly difficult, and not without its risks. In 1960, a rocket launch in the Soviet Union killed around 160 people near the launchpad. In 1971, three cosmonauts died on Soyuz 11 after a faulty valve led to sudden decompression.

The Soviets also gained a reputation – not completely undeserved – of covering up incidents that embarrassed them and taking unnecessary risks.

So when the Judica-Cordiglia brothers claimed to have made recordings of supposed crewed missions by the Soviet Union, it's easy to see why people were receptive to the idea. The brothers claim to have recorded several missions by the Soviets that were not public knowledge, including a morse code SOS signal from a spacecraft that appeared to be moving away from Earth's orbit.

"It was going very, very fast," Giovanni Judica-Cordiglia told Vice, "and therefore it was moving away from the earth at escape speed. And so it made us think that rather than bringing the vehicle back to Earth…it was moving away from Earth into space."

One of their most famous recordings, supposedly taken in November 1963, claims to capture one of the "lost cosmonauts" as she re-enters the atmosphere, dying before she returned to the Earth.

The brothers claim that they did not speak Russian, and had to get translators (as well as ask their sister to learn Russian) to find out what they had recorded. The brothers maintain to this day that the recordings are genuine.

However, the "lost cosmonauts" theory may just be a conspiracy theory. Since the fall of the Soviet Union, disasters of the space program have come to light, such as cosmonaut Valentin Bondarenko's death during training, and the subsequent cover-ups revealed. No details of lost cosmonauts, or anything that would verify these recordings and other stories, have been found.

Some believe the Judica-Cordiglia brothers fabricated the recordings entirely. Space journalist and historian James Oberg notes that no corroborating evidence to these claims exists, and lists a few other problems with claims by the brothers, which might cast doubt on their authenticity. Among these were claims (published later in a book) that the brothers had been able to listen into the Mercury 6 spacecraft.

"No verifiable evidence that signals directly from the Mercury-6 (John Glenn) spacecraft in February 1962 were actually received by the brothers, especially since the orbit of the spacecraft was at all times far out of range of Italy," Oberg wrote. "The claim that they determined the secret radio frequency from a photograph of an antenna is not convincing since the antenna they refer to is a postlanding rescue beacon, not even deployed or activated until after the capsule was in the water."

Claims that the brothers heard signals from Yuri Gagarin's spacecraft were also doubted by Oberg, "especially since the orbit of the spacecraft was at all times out of range of Italy and during the minutes of closest approach, on its way back to Earth, the spacecraft was undergoing deceleration and plasma blockage of radio." 

"No evidence for supposed deaths of cosmonauts on these early space missions can stand up under serious scrutiny today," Oberg wrote in a long piece debunking the "lost cosmonaut" theory.

"The blame for the fact that these stories spread and thrived in the early 1960's must rest squarely on the shoulders of the Soviet news managers. Their publicity policy of evasions, boasts, distortions and outright lies created the atmosphere of mystery and secrecy out of which all sorts of sensational and outrageous stories grew."