Gagarin died exactly four decades ago, on March 27, 1968, a little under seven years after becoming the first human to fly to space and orbit the Earth. His death came during what should have been a routine practice flight in a MiG-15UTI fighter plane, which crashed near the town of Kirzhach in Central Russia.
Soviet officials made no official announcement as to the cause of the crash and all the details of the accident were archived and marked "Top Secret."
On Thursday, a Russian Air Force official rejected suggestions that a new probe should be launched into Gagarin's death, saying: "No additional investigation is necessary." The Kremlin also turned down an appeal for the case to be reopened in 2007.
The Air Force official also categorically rejected calls for the hermetically-sealed barrels containing the fragments of Gagarin's plane to be reopened.
However, despite top-level reluctance to look into the causes of the accident, even during Soviet times there were whispers and rumors that the cosmonaut's death was due to something more than a routine training flight gone wrong. Although Gagarin was in the process of retraining as a fighter pilot when his plane went down, both he and his instructor, Vladimir Seryoghin, were hugely experienced pilots.
The theories as to the 'true' cause of the crash ranged from the plausible to the outlandish: in 1986, a belated inquest suggested that the afterburners of a passing jet may have caused the crash. Others alleged that the then Soviet leader, Leonid Brezhnev, had ordered Gagarin's death due to feelings of envy over the charismatic cosmonaut's popularity.
Fringe theories had it that Gagarin had been taken away by aliens, while another theory, voiced in the 1990s by Finnish conspiracy theorists, claimed that Gagarin had never been in space and that the whole thing had been an elaborate Soviet propaganda exercise. Gagarin was murdered, they said, to protect the secret.
Following the tragedy, Gagarin and Seryoghin were buried in the Kremlin walls, an honor reserved for the communist state's most respected and famous citizens. Gzhatsk, a town in the Smolensk Region, was also renamed after Gagarin.
Gagarin left a wife and two daughters, and perhaps the most fitting tribute to the Soviet cosmonaut can be found in the letter he wrote to them before his momentous 1961 flight into space. Although he said he implicitly "trusted the technology" that was to take him on his momentous journey, he wanted to leave a message to his family in case something went wrong. After all, as he said in the letter, anyone of us might "get knocked down by a car tomorrow."
"I have lived honestly," he wrote, "and tried to bring some benefit to other people, small as this may be. I read sometime during my childhood the words of V.P Chkalova [the Soviet pilot who first flew non-stop across the North Pole] -'If you are going to be - be first.' I have tried to do this and will go on trying."
Forty years after Gagarin's death and less than 24 hours after the Endeavour space shuttle returned from its mission to the International Space Station, the legendary Soviet cosmonaut's feats may seem technically humble in comparison to the lengthy spacewalks carried out by today's astronauts. However, Gagarin himself realized that space travel would continue to progress, and that his mission was just the first step, writing in his 'farewell' letter: "This is history! The start of a new era!"