Cosmonaut German Titov, Moscow's second man in space and the first person to spend more than a day in orbit, was found dead in his home sauna, police said on Sept. 21. He was 65.
A police spokesman said that law enforcement's early hypothesis was that Titov probably died of carbon monoxide poisoning late the night before.
Gennady Seleznyov, speaker of the State Duma lower house of parliament, where Titov was a Communist deputy, said the ex-cosmonaut may have suffered a heart attack.
On Aug. 6 and 7, 1961, Titov spent 25 hours 18 minutes on board the tiny Soviet Vostok-2 spacecraft, in what was the first full-scale space mission after two mostly symbolic space flights by a Russian and an American.
On April 12 that year, Yury Gagarin made the first flight on Vostok-1, which lasted less than two hours.
Titov was the backup cosmonaut for that flight, and Western reports have suggested he only narrowly missed being chosen to go up first instead of Gagarin.
Gagarin's mission was followed by a 15-minute sub-orbital flight by U.S. astronaut Alan Shepard.
Titov recently threw himself into politics and represented the Communist Party in the defense committee of the State Duma.