Riot police were called to calm massive riots that broke out in Moscow over the weekend that highlighted a simmering racial tension between ethnic Russians and Muslims from the Caucasus that's always threatening to boil over.

Police arrested hundreds of people after Yegor Shcherbakov, a 25-year-old ethnic Russian, was killed in Moscow's Biryulyovo district on Sunday. The Associated Press says Shcherbakov was stabbed after a dispute erupted over his girlfriend while the couple was walking home on Thursday. Local media released a photo of the suspect, a man described as having a "non-Slavic appearance." Many Russian citizens concluded that the culprit was a Muslim migrant from the North Caucasus and started a relatively peaceful protest. Things eventually got out of hand when a small group started smashing windows in a shopping mall and raiding a vegetable stand that's known to employ many migrant workers. The group becoming increasingly unruly, smashing anything in sight, overturning cars, throwing hammers at police and chanting racist slogans just a few blocks away from the Kremlin. 

Many have called Sunday's riots the worst case of anti-migrant anger in three years, reigniting a longstanding distrust of a region that been the home of a lengthy and bloody separatist movement since the fall of the Soviet Union. As reuters explains further

The rioting in Biryulyovo was the worth outbreak of unrest over a racially charged incident in Moscow since December 2010, when several thousand youths rioted just outside the Kremlin.

The youths clashed with police and attacked passersby who they took for non-Russians after the killing of an ethnic Russian soccer fan was blamed on a man from the North Caucasus.

Riot police were eventually called to rein in the very violent demonstrations. The number of people reportedly arrested varies, but the BBC puts it close to 1,200. Though it should be noted that Russian police still haven't identified what charges they'll bring against any of the people arrested during the riots, saying only that they're investigating "involvement in criminal activity."