After eight years Valentin Danilov still protests his innocence.
"I would really appreciate it if somebody finally told me what state secret I sold," Danilov told reporters, according to Reuters.
Though acquitted in 2003, Danilov, then professor at Russia's Krasnoyarsk Technical University, was retried and convicted in 2004 for selling state secrets to China.
Danilov said he had sold satellite technology to a Chinese company, but as the Guardian points out, he also said the technology was publically accessible.
Many human rights groups condemned Danilov's imprisonment. The Associated Press reports Danilov will take his case with the European Court of Human Rights.
Speaking to reporters, Danilov voiced criticism of Russia's judicial system.
"The problem is not one of law but of how the judging is done," he said, according to Reuters. "We have three branches of power - the legislative, the executive and the judiciary. It's a fight between the legislative and executive with the court in between. They should pull in different directions so that the court works well, but if they all pull in only one direction, then what?"
In prison Danilov wrote a blog Radio Free Liberty. In his last post, on November 9, 2012, wrote about the trial and conviction of the feminist anti-Putin protest group Pussy Riot.
"The trial of Pussy Riot ended with harsh sentences that defy understanding," he wrote. "Is the goal to intimidate? It's unlikely to work."
Three Pussy Riot members were sentenced to two years in prison for singing an anti-Putin song in a Russian Orthodox Church in Moscow. One member was recently released.
It's ironic that Danilov's release comes just ten days after Russia passed a law expanding the definition of treason, which human rights groups say could be used to brand a traitor anyone the Kremlin doesn't like.
Now on parole, Danilov said he would like work again. But not in anything connected with space.
"Everything that's connected with space, everywhere it's a state secret," he said, according to Reuters.