MOSCOW -- A world martial arts champion from Russia's southern Caucasus region was convicted Tuesday of involuntary manslaughter but set free after a trial that inflamed the country's ethnic tensions.
The verdict led to protests by nationalists outside the court and prompted Russian riot police to flood the wide square outside the Kremlin to prevent possible violent clashes between nationalists and ethnic minorities from the Caucasus.
Rasul Mirzayev had punched former police student Ivan Agafonov outside a Moscow nightclub in 2011 after the drunken 19-year-old offended Mirzayev's girlfriend. Agafonov fell down, hitting his head on a sewer grate and dying four days later.
Mirzayev's trial had raised the anger of nationalists, who accused him of deliberately killing the Russian student. The athlete's supporters argued that Agafonov had provoked the lethal punch and his killing was accidental.
The Zamoskvoretsky court ruled Tuesday that since Mirzayev had already served his sentence in pre-detention he could walk free.
There are significant tensions between ethnic Russians, who make up two-thirds of the country's 142 million people, and the more than 100 ethnicities that account for the remaining third. Hundreds of thousands of Caucasus natives have flooded central Russia in search of jobs, triggering widespread xenophobia and a spike in hate crimes.
Mirzayev, a bearded and lean 26-year-old, hails from Dagestan, Russia's most multiethnic province. Dagestan has for years been an epicenter of Islamic insurgency that stems from separatist wars in neighboring Chechnya.
The Caucasus has also been beset by high unemployment and rampant corruption. The Kremlin has poured billions of dollars to subsidize the restive region, but government critics say most of the money is being embezzled by local leaders.
Polls show that nearly half of Russians resent Kremlin's subsidies to the region and dislike migrants from both the Caucasus and the former Soviet Central Asian states.
A protest led by neo-Nazi leader Dmitri Demushkin erupted outside the court building Tuesday. Moscow police said six protesters, including Demushkin, were detained, while several dozen other protesters chanted "Shame!" A similar protest took place in the western Siberian city of Novosibirsk.
Dozens of riot police also gathered at Manezhnaya Square outside the Kremlin and blocked adjacent areas to prevent a nationalist rally. Last year, thousands of ultranationalists clashed with police and beat dark-skinned passers-by there to protest the shooting of a Russian soccer fan by a group of Caucasus men.
A top human rights advocate urged Russians not to escalate ethnic tensions following Mirzayev's release.
"There is no need to turn this everyday conflict into an inter-ethnic collision," Mikhail Fedotov was quoted by the Interfax news agency as saying.
But thousands of angry comments made the conviction one of the top Twitter hashtags in Russia.
"Such verdicts might trigger a social explosion," opposition leader and outspoken Kremlin critic Vladimir Milov tweeted.
Other comments suggested that Mirzayev's release was prompted by pressure from the Kremlin and Caucasus leaders.
"The regime is more afraid of a small riot in the Caucasus than a big one throughout Russia," opposition activist Nikolai Permyakov tweeted.
Even a democratic activist like Alexei Navalny has urged the Kremlin to "stop feeding the Caucasus" and was one of the organizers of this year's Russian March, a rally of ultranationalists that also drew neo-Nazis, monarchists and militant Orthodox Christians.