Yuri Gagarin, the first man in space, died in a plane crash 45 years ago. The official explanation from Soviet authorities was that he crashed trying to avoid foreign objects, like birds. That idea never sounded right to pilots, and now we know what really killed the first man in space.

On March 27, 1968, Gagarin and his flight instructor Vladimir Seryogin took off for a flight about a MIG-15, an early Soviet jet fighter that first flew in 1947. The pair were flying near the town of Novoselovo, 55 miles from Moscow, when they went down.

The official explanation was that the plane encountered a "foreign object" like birds or a hot air balloon. However, Alexey Leonov, a cosmonaut like Gagarin, claims that the object that caused Yuri's crash was not birds or a balloon, but another jet.

"We knew that a Su-15 was scheduled to be tested that day, but it was supposed to be flying at the altitude of [33,000 feet] or higher, not [1500-1600 feet]. It was a violation of the flight procedure," Leonov said. The Su-15 is a newer supersonic interceptor jet first introduced in 1967.

Jet planes can crash if another jet passes too close it it, causing the first airplane to flip over. This explanation is the only one fits the flight data related to the crash, according to the first space-walker.

"While afterburning, the aircraft reduced its [position relative to the other plane] at a distance of [30-50 feet] 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 [470 miles per hour]," Leonov said. 

Leonov had his own big accomplishment in space, when he became the first person ever to perform a spacewalk, in 1965. He was flying a helicopter in the area on the day when Gagarin was killed, and heard the two explosions as both planes crashed. Leonov was also part of the commission investigating the incident in the immediate aftermath of the event.

Gagrin's first flight into space took place on April 12, 1961, during which the cosmonaut completed one orbit of the Earth before landing.

Leonov was allowed by the Russian government to reveal what he knows of the crash that killed Yuri with one exception - the name of the Su-15 pilot who survived the crash and is now 80 years old.

A new Russian film, Gagarin: First Man in Space, is the first full-length video documentary on the pioneering space traveler produced in the astronaut's native country.