There were moments during the trial of Alexei Navalny, leader of the Russian opposition movement, when his dark realism seemed to lift, allowing him to believe that the Kremlin would not go so far as to throw its fiercest critic in prison. When we spoke on the phone days before his verdict was read on Thursday he told me, “It sounds crazy, but they seem serious about letting me run for mayor.” The incumbent mayor of Moscow, a diehard ally of Russia’s President Vladimir Putin, even helped Navalny get on the ballot this week. It had been Navalny’s intention to run in the election in September. But that was all for nothing; on Thursday morning Navalny, together with a co-defendant, was found guilty of embezzling nearly $500,000 during a timber-trading deal. Navalny was sentenced to five years in prison. His co-defendant, businessman Pyotr Ofitserov, was given a four-year sentence. Each man was fined over $15,000.

The ruling, which will likely keep Navalny locked up until the end of Putin’s third term in office and which Navalny will almost certainly appeal, seemed to have no logic other than the one Navalny expressed to me just before the trial began. “‘If you don’t believe we’ll throw you in prison, you better believe it,’” he told me while pacing around his office in April. “That’s Putin’s position,” he said.

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But it didn’t have to be. As Navalny was first to admit, his ability to challenge Putin’s rule could have been crushed without the use of Russia’s prison camps. The justice system could have sidelined him with a simple guilty verdict on charges of embezzlement, which even the investigators on the case admitted to have political motives. The court could have given him a large fine and a lengthy period of probation. That would have put a felony charge on his record, barring him from ever running for office in Russia again. And if he continued to organize or even attend unsanctioned political protests — like the one last winter that he says brought down the Kremlin’s fury — it would constitute a violation of his probation and would likely result in his getting sent directly to jail. His options for political activism would thus be isolated mostly to the Internet — to his Twitter account and hugely popular blog.

Navalny was already weakened in other ways. He was almost bankrupt by this spring, hardly able to work on his anticorruption campaigns because of all the time and money he was spending on the trial. And worst of all for him, the popular movement against Putin was losing energy by the day, as Navalny’s fellow activists bickered among themselves, split off and seemed at times to resign themselves to Putin’s rule.

So why imprison a man who already poses no real threat? As Navalny noted, it would only be to make a statement: “‘If you think we’re afraid of the West or the press … here’s another set of charges.’” That is the message Putin has sent time and again. And although the Russian constitution bestows the courts with full independence, rights groups have for years chronicled their use in Russia as a weapon of the ruling elite. During Putin’s first term as President, his greatest political enemy, the oil baron Mikhail Khodorkovsky, was sent to prison, where he remains to this day. Last summer, a Moscow court sentenced members of the protest group Pussy Riot to two years in prison for hooliganism after they performed a crude anti-Putin song near the altar of a cathedral.

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Russian accountant Sergei Magnitsky, who had accused a group of officials of large-scale fraud, not only died in prison in 2009 but also was convicted this month of tax evasion after his death, the only posthumous guilty verdict ever handed down in Russian history. Right now a group of activists are also on trial in Moscow for taking part in a political protest that turned violent last May.

But if all the previous cases have been met with dejection, deepening the cynicism and political malaise that has gripped the anti-Putin movement, the imprisonment of Navalny could mark a turning point. Minutes after the verdict was announced, activists began calling for a protest at the Kremlin walls, and riot troops began erecting barriers to keep Navalny’s supporters away. They were, in effect, reacting to Navalny’s final message, which he tweeted out just before the cuffs clicked onto his wrists: “You guys don’t go missing me,” he wrote to his 370,000 followers. “And most important — don’t be lazy.”

It was a lot to ask of a movement, which, after a year of lost momentum, is now also robbed of its leader. The demonstrations of 2011 and 2012, when Navalny led hundreds of thousands of protesters in demanding Putin’s resignation, have devolved into rote and repetitive affairs. But now, thanks to the Russian justice system, that movement will have a martyr to rally around. The Kremlin must have seen this coming, and it will now have to face the backlash.