The Investigative Committee said in a statement that Djalilov "carried out an explosion" in the carriage of a train travelling between two busy stations yesterday afternoon.
Djalilov's "genetic trace" was also found on a bag containing a second bomb left at another metro station and later defused, the statement said.
Investigators gave no further details about Djalilov but his name and year of birth coincided with a statement from the Kyrgyz security services which said earlier today he was a naturalised Russian citizen originally from Kyrgyzstan.
Flags flew at half-mast in Russia's second city and flowers and candles piled up at an impromptu memorial outside the metro station rocked by the attack, as authorities beefed up security on the busy underground transport system.
The Kremlin said the bombing was "a challenge to every Russian", including President Vladimir Putin.
The bombing raised jitters ahead of the Confederations Cup football tournament in June, with the opening game and final set to be held in Saint Petersburg as Russia gears up towards hosting the World Cup next year.
"Everyone in the metro can only think of this," said 45-year-old Svetlana Golubeva as she entered the underground.
Resident Dmitry Leonov said there was a sense of shock that terror could strike the city as he picked his way through the candles and flower tributes lining the gates of the station.
"Now we're all under threat," he said.
Putin, who hails from Saint Petersburg, was holding a meeting near the city at the time of the bombing and later yesterday added his own floral tribute at the scene.
A spokesman for Kyrgyzstan's security services, Rakhat Sulaimanov, told AFP in Bishkek that authorities of the ex-Soviet republic were in contact with their Russian counterparts over the case.
There has not been a claim of responsibility for the attack, which came after the Islamic State group called for attacks on Russia in retribution for its military intervention in Syria against the jihadists.
Russia has long been battling an Islamist insurgency in its volatile Caucasus region and has suffered a string of bloody terror attacks over the years.
Those hurt include citizens of Belarus, Kazakhstan and Uzbekistan, as well as Russians from 13 different regions, according to the Saint Petersburg authorities.
The chief of the Saint Petersburg metro, Vladimir Garyugin, said today that quick actions by staff prevented a much higher toll and that passengers had helped each other instead of panicking.
The second bomb was an explosive device fashioned from a fire extinguisher and hidden in a bag, he said.
In the wake of the attack Putin spoke to a string of leaders around the globe -- including holding only his second phone call with US President Donald Trump overnight.
Trump offered Putin the "full support of the United States Government," according to a White House statement.
Putin also talked up cooperation in the fight against terrorism with leaders in Germany, France, Turkey and the king of Saudi Arabia.
The attack in Saint Petersburg is the first in several years to hit a major city in Russia.
Russian ground transport has also been hit by extremists before, including in the Moscow metro and the Domodedovo airport, where a blast claimed by Islamic insurgents killed 37 people in 2011.
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