detected the open vent and followed procedure by executing a rapid dive to a lower altitude. This dive caused them to lose consciousness and crash. On 12 April 2007, the Kremlin vetoed a new investigation into the death of Gagarin. Government officials said they saw no reason to begin a new investigation. In April 2011, documents from a 1968 commission set up by the Central Committee of the Communist Party to investigate the accident were declassified. The documents revealed that the commission's original conclusion was that Gagarin or Seryogin had manoeuvred sharply, either to avoid a weather balloon or to avoid "entry into the upper limit of the first layer of cloud cover", leading the jet into a "super-critical flight regime and to its stalling in complex meteorological conditions". Alexei Leonov, who was also a member of a state commission established to investigate Gagarin's death, was conducting parachute training sessions that day and heard "two loud booms in the distance". He believes that a Sukhoi Su-15 was flying below its minimum altitude and, "without realizing it because of the terrible weather conditions, he passed within of Yuri and Seregin's plane while breaking the sound barrier". The resulting turbulence would have sent the MiG-15UTI into an uncontrolled spin. Leonov said the first boom he heard was that of the jet breaking the sound barrier and the second was Gagarin's plane crashing. Awards and honours Medals and orders of merit On 14 April 1961, Gagarin was honoured with a parade attended by millions of people that concluded at the Red Square. After a short speech, he was bestowed the Hero of the Soviet Union, Order of Lenin, Merited Master of Sports of the Soviet Union and the first Pilot-Cosmonaut of the USSR. On 15 April, the Soviet Academy of Sciences awarded him with the Konstantin Tsiolkovsky Gold Medal, named after the Russian pioneer of space aeronautics. Gagarin had also been awarded four Soviet commemorative medals over the course of his career. He was honoured as a Hero of Socialist Labour from Czechoslovakia on 29 April 1961, and Hero of Socialist Labour (Bulgaria, including the Order of Georgi Dimitrov) the same year. On the eighth anniversary of the beginning of the Cuban Revolution (26 July), President Osvaldo Dorticos of Cuba presented him with the first Commander of the Order of Playa Girón, a newly created medal. Gagarin was also awarded the 1960 Gold