New details emerge about crash that killed Yuri Gagarin, first man in space

Famous Russian cosmonaut Yuri Gagain was the first man in space — but the interstellar pioneer died mysteriously in 1968, after the MiG-15 he was flying went down not far from Moscow.

Now, fellow cosmonaut Aleksey Leonov, the first man to conduct a spacewalk, has been allowed to come foward to reveal what was likely the real cause of Gagarin's fatal crash: a supersonic Su-15 jet appears to have been flying too low, coming close to Gagarin and his flight instructor's jet, and sending the two men into a fatal spiral. 

"We knew that a Su-15 was scheduled to be tested that day, but it was supposed to be flying at the altitude of 10,000 meters or higher, not 450-500 meters. It was a violation of the flight procedure," Leonov told Russia Today. 

"While afterburning the aircraft reduced its echelon at a distance of 10-15 meters in the clouds, passing close to Gagarin, turning his plane and thus sending it into a tailspin — a deep spiral, to be precise — at a speed of 750 kilometers per hour," Leonov said. 

More from GlobalPost: First woman in space celebrates 50-year anniversary

Leonov initially heard two booming sounds during the incident, and thought that one was the sound of a jet breaking the sound barrier, while another was the sound of Gagarin's craft hitting the ground.

After seeing a new declassified report on the crash, Leonov discovered the booms were only about 2 seconds apart, not the 15 to 20 he had estimated before.

"That suggested that the two jets must have been no less than 50 kilometers apart," he said.

The pilot of the Su-15 is still alive at 80 and remains unnamed, as a condition of Leonov being allowed to come forward. 

Why all the secrecy?

"My guess would be that one of the reasons for covering up the truth was to hide the fact that there was such a lapse so close to Moscow," noted Leonov.

Many theories were put forth over the years to explain the death of Gagarin, ranging from tales of the cosmonaut and his flight instructor taking potshots at deer from the cockpit, to intoxication, to a sudden attack by space aliens. 

The news comes days after the 50th anniversary of the lift-off of Valentina Tereshkova, the first woman in space.