The bomber, Akbarzhon Dzhalilov, had lived in St. Petersburg for several years, working as a car repairman and later at a sushi bar. Pages on his social media networks reflected his interest in radical Islam and boxing, but those who met Dzhalilov described him as a calm and friendly man.
Russia's health minister raised the death toll to 14, including the bomber. About 50 others remained hospitalized, some in grave condition. Many were students heading home Monday after classes on one of the city's busy north-south lines.
Before Dzhalilov traveled to St Petersburg where he eventually got Russian citizenship, his ethnic Uzbek family lived in Osh, the city in southern Kyrgyzstan that saw more than 400 people killed and thousands injured in clashes between ethnic Kyrgyz and minority Uzbeks in 2010.
St Petersburg has a large diaspora of people from Kyrgyzstan and other mostly Muslim former Soviet republics in Central Asia. They have fled ethnic tension, poverty and unemployment for jobs in Russia.
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Russian media said Dzhalilov worked with his father in a car repair shop and then became a cook at one of the city's many sushi bars. He stayed in St Petersburg when his parents moved back to Kyrgyzstan.
One former colleague at the sushi chain described Dzhalilov, who turned 22 on Saturday, as "a very kind person."
"He was a non-conflict person. We didn't expect to hear such news today," said the woman, who spoke on condition of anonymity because she feared for her personal safety. Neighbors in Osh also described him as a nice and friendly man.
Security cameras caught the bespectacled Dzhalilov as he entered the subway, appearing calm and clad in a red parka with a fur collar and blue wool hat.
He wore a backpack believed to hold the bomb that was loaded with metal balls and screws for maximum damage.
The Investigative Committee, Russia's top investigative agency, said it also found Dzhalilov's DNA on a bag with a similar bomb that was found and deactivated at another subway station shortly after the blast.