Unconfirmed reports in local media say he moved to St Petersburg with his parents in 2011, and remained in the city after they later returned to Osh.
Very little is known about Jalilov's background before he carried out the attack.
Unconfirmed reports in Russian media said he worked for some years as a sushi chef in a St Petersburg restaurant and was a martial arts fan, citing a profile on Vkontakte, a Russian social network.
CCTV images of the suspect, provided by police to Russian television channels and redistributed by Reuters, show a young man in a red parka and carrying a rucksack walking through a metro station.
Where is he from?
Kyrgyzstan, a mountainous former Soviet republic sandwiched between Tajikistan, Kazakhstan, Uzbekistan, and China, is a Muslim-majority country closely allied with Russia.
Jalilov is an Uzbek, not Kyrgyz name.
Osh, the city the family comes from, was the scene of bloody clashes between Kyrgyz and Uzbek communities in 2010. Some have speculated the family moved to escape the violence, and might provide a clue to his path to radicalisation.
Why did he do it?
No group has yet claimed responsibility for the attack and the suspect's motives remain unclear.
Russia's Interfax news agency cited law enforcement sources saying Jalilov was linked to known Islamist extremists - but it offered no details.
Most Islamist terrorist attacks in Russia have been carried out by people from the North Caucasus republics, where an insurgency has raged since the Chechen Wars of the 1990s and 2000s.
While Jalilov may be the first Central Asian attacker, it follows a trend of radicalisation in the region.
Like other former Soviet republics, including Russia, Kyrgyzstan has seen numbers of radicalised youth heading to Syria and Iraq to fight with Isis (Islamic State) and other extremist groups.
Last year Kyrgyz authorities said up to 600 citizens had travelled to Iraq and Syria. Some have been used as suicide bombers there.
