A man suspected of killing 14 people in a suicide bomb attack on St Petersburg's metro may have travelled to Syria before the attack, it has been claimed.
Two former colleagues of Akbarzhon Jalilov, 22, say he developed an interest in Islam and soon after travelled to Turkey in 2015.
Not much is known about the terror suspect's movements between then and the start of this year, as friends say he seemed to disappeared.
His journey to Turkey has raised questions about whether he had travelled to Syria during that gap in time or met with anyone linked to a terror group.
Jalilov's former colleagues at a sushi restaurant in St Petersburg told Reuters that there was talk that he had travelled to Syria, but they did not know for sure if he visited the war-torn country.
Radical Islamists use Turkey as a route into parts of Syria that are controlled by ISIS.
Jalilov was born in 1995 and grew up in the city of Osh in Kyrgyzstan, a mainly Muslim ex-Soviet Republic in Central Asia.
Police believe he was the man who blew himself up inside a St Petersburg metro station, killing 14 people, as Russian President Vladimir Putin visited the city last Monday.
No group has claimed responsibility for the attack, although Russia has been threatened by ISIS in the past.
Former acquaintances of Jalilov say he moved to St Petersburg in 2011 and worked low-paid jobs.
He was a chef at a Sushi Wok restaurant, where a former colleague, who was also from Osh, described him as an even-tempered man who didn't drink or curse when they worked together in 2014.
The former colleague didn't notice any signs of extremism, adding: "I would have said firmly that Akbar was not capable of doing anything bad."
The ex-colleague said Jalilov developed an interest in Islam in 2014, and began praying, going to a mosque, reading the Koran and growing a beard.
Another native of Osh, who also worked with Jalilov in St Petersburg, said the suspect travelled to Turkey in November 2015 to join his uncle in Antalya.
However, Jalilov's uncle, Khasan Kuchkarov, told Reuters he had lived in Antalya but left in September 2015 to return to Osh and was unaware of Jalilov travelling there.
Jalilov reappeared when he visited Osh in February.
The following month he returned to St Petersburg and rented an apartment where he was living at the time of last week's attack.
Russian officials declined to comment to Reuters about Jalilov's travel history.
