Investigators say they have searched the home of the suspected suicide bomber behind Monday’s deadly explosion on the St. Petersburg subway, and Russia’s president said the blast showed terrorism is still a real threat in his country.

The bomb went off on a train under Russia’s second-largest city on Monday, killing 14 people and injuring dozens. Investigators said they suspect a 22-year old Kyrgyz-born Russian citizen, Akbardzhon Dzhalilov, of having detonated the bomb.

It went off as the train was moving between two stations. One was closed by a bomb threat Tuesday and again on Wednesday as officials checked for anything suspicious.

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Russia’s top investigative body, the Investigative Committee, said in a statement in the early hours Wednesday that investigators had searched his home in St. Petersburg. They also examined CCTV footage from outside the home they say shows him leaving home with a bag and a backpack.

Another bomb, hidden in a bag, was found and de-activated at another St. Petersburg station just half an hour before the blast. Dzhalilov’s DNA was found on the bag, authorities say.

Dzhalilov’s parents arrived in St. Petersburg for questioning Wednesday. State-owned Rossiya 24 television showed footage of a middle-aged woman in a red coat and a white headscarf and a man in a black jacket, chased by journalists.

Dhzalilov, 22, is believed to have moved to St. Petersburg from the Central Asian nation of Kyrgyzstan when he was a teenager.

Russian President Vladimir Putin told security officials from a regional alliance Wednesday that the subway bombing underlines that terrorism’s threat isn’t subsiding.

Putin met Wednesday with heads of the security services from the Commonwealth of Independent States, a grouping of most former Soviet republics.

“We see that, unfortunately, the situation is not improving. The recent tragic events in St. Petersburg are the best confirmation of this,” Putin said. “We know that each of our countries, practically every one, is a possible and potential target of terrorist attacks.”

The Investigative Committee also said Wednesday that six people had been arrested in St. Petersburg on suspicion of “aiding terrorist activities.”

The six come from former Soviet Central Asian republics. The investigators suspect that they have been recruiting Central Asian men to join the ranks of the Islamic State of Iraq and Syria (ISIS) and other extremist organizations in St. Petersburg since November 2015.

But the Wednesday statement said, “At this moment, the investigators have no evidence of connection or acquaintance of the detained with executor of the terrorist action in the St. Petersburg metro (subway).”