Russia's FSB security service said today that it was close to having identified who ordered the bombing on the Saint Petersburg metro this month that killed 14 people.
FSB head Alexander Bortnikov told reporters that the identity had been "practically established," Russian news agencies reported.
It was not immediately clear if Bortnikov was referring to a group or an individual.
Authorities have attributed the attack to 22-year-old Akbarjon Djalilov, thought to be a Russian national born in Kyrgyzstan, who died in the blast.
There has been no claim of responsibility but investigators say they are examining possible links to Islamic State jihadists.
The FSB has detained another man born in Kyrgyzstan on suspicion of helping orchestrate the metro bombing, who admitted to "some involvement" in the crime during a court appearance Tuesday.
Eight other people - all from mainly Muslim Central Asian countries - have also been detained in Moscow and Saint Petersburg over alleged involvement in the attack.