[Breaking news update at 3.01 a.m ET]
The suspect in Monday's train explosion in St. Petersburg, Russia, which killed 11 people and injured dozens, has been identified as Akbarjon Djalilov, according to Kyrgyz security services and quoted by several news agencies. The suspect is a Kyrgyzstan national.
[Previous story, published at 2.26 a.m. ET]
Russian commuters took pause Tuesday near makeshift memorials that had sprung up since since Monday's deadly subway attack.
Amid an increased police presence, St. Petersburg authorities attempted to instill a sense of normalcy following the bombing between the Sennaya Ploshchad and Tekhnologichesky Institut stations that ripped apart a train car, killing 11 people and injuring dozens more.
Here are the latest developments:
The two city center stations have been reopened. A three-day mourning period has started. No group has claimed responsibility for the attack, which led to the shutdown of the city's metro system. 11 people were killed and 51 people were injured in attack, according to CNN affiliate RBC. Four of the injured are in critical condition, Health Minister Veronika Skvortsova said, according to Tass. According to Kremlin spokesman Dmitry Peskov, Russian President Vladimir Putin held a meeting with security and law-enforcement services on Monday where he was informed about preliminary results of the investigation over the metro blast, state-run Tass news agency reported. Putin, who had been in St. Petersburg earlier in the day, laid roses at one of the memorials Tuesday. US President Donald Trump spoke briefly with Putin on Monday, expressing his condolences in the wake of the terror attack and offering assistance in the investigation.
A second, larger device was found and defused at another station, Russia's Anti-Terrorism Committee said.
That device, hidden in a fire extinguisher, was larger than the one that went off, according to state media reports quoting law enforcement. It carried about a kilogram of TNT, the reports said.
No claim of responsibility
Russian Prime Minister Dmitry Medvedev described the attack as a "terrorist act," but authorities have released no specifics on who they believe is responsible, and no group has yet claimed the attack as their handiwork.
However, the two main suspects appear to be Chechen separatists, and ISIS, the Iraq and Syria-based group which famously claimed to bomb a Russian MetroJet flight over the Sinai desert in Egypt.
Another possibility, says former CNN Moscow Bureau Chief and Woodrow Wilson Center Global Fellow Jill Dougherty, is a hybrid Chechen rebel-ISIS attack.
"It could (be a combination of ISIS and Chechen separatists)," she told CNN.
Many Chechen fighters have gone to fight in Syria, she says, and it has long been feared that they could bring their battlefield expertise back home.
"The fear was that after (Chechens) had been radicalized and almost professionalized, by that time in Syria would then come home and carry out attacks in Russia ... (which) would fit the kind of ISIS international terrorism theory that Putin has been talking about.
"It makes it easier for him to make that proposal... to President Trump and the West -- 'let's get on board, lets fight terrorism together.'"
Russia was once a hotspot for terror attacks, but the country has experienced relatively few in recent years.
In December 2013, a suicide bombing at a train station in Volgograd killed at least 16 people. The following day, in the same city, a suicide bombing on a trolley bus killed 14 people.
In 2010, two female suicide bombers linked to the Chechen insurgency blew themselves up at two Moscow metro stations, killing 40. In 2002, Chechen rebels killed 170 hostages in a theater in the capital, Moscow.
Attack unlike ISIS' usual MO
However, former FBI special agent Bobby Chacon says that to stay silent after an attack goes against the ISIS modus operandi.
"The first thing that's missing from an investigator's perspective is the claim of responsibility," he told CNN.
"Last year when two ISIS operatives attacked police officers on the outskirts of Moscow... one of the first things that was released was the video where they claimed allegiance to al Baghdadi, the ISIS leader and ISIS itself and that's a hallmark, as we've seen in San Bernardino, of an ISIS attack."
There are fears by critics of the Russian government that the Kremlin would use the incident to crack down on anyone seen as responsible or linked to the bombing.
Chairman of the Human Rights Foundation, former chess champion and Putin critic Garry Kasparov commented on Twitter that the incident took place at a time of internal strife in Russia, with increased protests in Moscow and across the country challenging Putin's government.
"Tragedy in St. Petersburg," he wrote. "Once again 'unknown terrorists' perfectly timed to serve Putin's political agenda. Forget protests, back to fear."
However, Chacon says that Putin doesn't need a "pretext" to enact the kind of crackdown that Kasparov says is impending.
"I don't think Mr. Putin needs a pretext. If he wants a crackdown on his people he's shown in the past a tendency to do that without any kind of pretext," he said.