Although 14 people have died, the attack could have been much worse. I was on this same St. Petersburg metro line at 8:30 that morning, heading to the station to take a train back to Moscow, and it was so packed I could barely squeeze into the subway car. If the bomb had gone off during the morning or evening rush hour, there would have been far more bodies lying on the platform. A second larger bomb was disarmed at another station.
But the casualty count alone doesn't tell the full story. Russia, a nation that had a brief respite from terror, is once again being awakened to dangers that were suppressed but never eliminated. And its people, who for the past few years have seemed not to notice or care, may now have to reckon with the potential threats that face it: A huge population of often mistreated migrant workers from Central Asia who can be susceptible to radicalization, an Islamist insurgency once again growing in the Russian North Caucasus and citizens reportedly returning home after fighting for the Islamic State.
"We used to think this wouldn't touch us, but now it's close by," a woman whose son was in a fast food restaurant across from the subway station during the attack told the news site Meduza. "Society should become vigilant. After (attacks in 2015 in) Paris I was afraid to go in the subway, and now I won't set one foot in it."
A friend in St. Petersburg told me there were few people in the subway on Tuesday morning, and those who were looked spooked. "Usually people are focused inward, they look at their phones or stare into space, but today everyone was looking around, looking at other people, seeing if there was anyone suspicious," he said. Though he predicted that in a few days it would once again be crowded with people absorbed in their phones.
Investigators have said the suspected suicide bomber is a 22-year-old Russian citizen born in Kyrgyzstan, a predominantly Muslim country in Central Asia.
Frequent in the 2000s, attacks by Islamic militants dropped off after the Sochi Olympics and the simultaneous crackdown on extremists in Russia's North Caucasus, including the once-restive Chechnya. But Monday's bombing suggested that Russia's momentary break from terror was over.
And that upsetting realization was shared across social media. Russians on Facebook and the Russian social network VK asked friends in St. Petersburg if they were safe, wrote messages of support and tried to organize free rides to get people home. One of my friends on Facebook wrote about the "uncontrollable paranoia" he was feeling about riding the subway.
Putin didn't even mention the bombing in the briefing after his meeting in St. Petersburg with Belarusian President Alexander Lukashenko. Instead, he announced they had ironed out their differences on the price of gas supplies. He later, however, laid roses outside the subway station where it happened.
There's a long history of such attacks in Russia, including bombings in the Moscow metro in 2004 and 2010, at Moscow's Domodedovo airport in 2011 and in a trolleybus and train station in Volgograd in 2013. The St. Petersburg metro previously suffered bombings in 1996 and 2007, and the country saw railroad attacks in 1997, 2007 and 2009.
That trend seemed to die out with the Sochi Olympics, when Russian special forces redoubled their offensive against Islamist militants in the North Caucasus and killed their leader Doku Umarov. The only major terrorist incident the country experienced after the Volgograd bombings was the downing of an airliner with 224 people, most of them Russian tourists, over Egypt in 2015, an attack claimed by ISIS.
I remember being surprised then that people on the street were discussing a possible connection between that attack and the start of Putin's air war in Syria, even though ISIS had declared jihad
against Russia (and America) earlier that month. State television, still the main source of news for most Russians, of course wasn't linking the issues, and Putin has claimed
that the country must fight terrorists in Syria to "prevent a threat to Russia itself."
If Monday's attack turns out to have been carried out by Islamist extremists, then it will be hard for Russians to pretend any longer that their terrorism problem has gone away.
For one thing, millions of migrant workers from Central Asia work in Russia. They are often young, impoverished and exploited by employers, making them a perfect audience for extremist messages. Many of the 2,000 to 4,000 Central Asians fighting for ISIS are believed to have been recruited in Russia.
Second, the Islamist insurgency in the North Caucasus has shown signs of a new flare-up. According to the respected Caucasian Knot website, the number of casualties from the conflict between Islamist militants and the security forces increased from 258 in 2015 to 287 in 2016.
"The news has been that the reality is getting better and better," said Caucasian Knot editor Grigory Shvedov. "But there is a need to recognize that things are not the same anymore, because of what we see in the North Caucasus ... There is a new wave of terror."
And third, between 2,500 to 7,000 Russian citizens are estimated to have gone to the Middle East to fight for the Islamic State. Moscow had reportedly
encouraged this exodus of militants to avoid attacks at the Sochi Olympics. But many are now returning to Russia.
According to Russia expert Mark Galeotti, the security services have been realizing they only postponed
the terrorism problem and that "sooner or later the militants -- now more experienced, battle-hardened, and maybe with new foreign friends and backers -- would be coming home."