MOSCOW/ST PETERSBURG • Akbarzhon Jalilov, the man suspected of blowing up a Russian metro train, represents a new wave of radical Islamists who blend in with local society, away from existing militant movements - making it harder for security forces to stop their attacks.
Jalilov's pages on the Russian equivalent of Facebook, VK, show his interest in Wahhabism, a conservative and hardline branch of Islam. But they give no indication that he might resort to violence, presenting a picture of a typical young man leading a largely secular life.
Fourteen people were killed and 50 wounded in the suicide bomb attack on Monday on a metro carriage in St Petersburg. Jalilov was also killed in the blast.
Russian state investigators said the suspected bomber was Jalilov, a 23-year-old born in the mainly Muslim former Soviet republic of Kyrgyzstan.
If radical Islam was indeed his motive, he will be distinct from two previous waves of attackers - those from Russia's restive North Caucasus region who fought successive rebellions against Moscow; and a later group who went to fight alongside the Islamic State in Iraq and Syria (ISIS) group.
THE NEW GENERATION
It's a completely different kind, a different level of terrorist threat from the one that Russian security services are used to dealing with. It's very difficult to counter things like this.
MR ANDREI SOLDATOV, a Russian expert on the intelligence services, on the new generation of Islamists who do not have a trail of arrest warrants which security forces usually rely on.
The new generation may take inspiration or instruction from people involved in those previous fights, and are drawn from the same Muslim communities.
However, they are not directly linked to those militant organisations, and have not created the trail of arrest warrants, tapped phone calls, travel documents and monitored border crossings, which security forces usually rely on to keep tabs on violent Islamist radicals.
"It's a completely different kind, a different level of terrorist threat from the one that Russian security services are used to dealing with," said Mr Andrei Soldatov, a Russian expert on the intelligence services.
Security services typically look for an organisation and financing network behind a terror attack, he said, but those may not exist in cases such as the metro bombing.
"It's very difficult to counter things like this," Mr Soldatov said.
British police have run into similar problems investigating the case of Khalid Masood, who sped across Westminster Bridge in a car last month, killing three pedestrians and injuring dozens more, before stabbing a policeman to death.
Shot dead by police, Masood also had no known links to militant groups.
Jalilov is typical of millions of young Muslim men living in Russia, some from the country's North Caucasus region and others, Muslim migrants from Central Asia.
Jalilov, an ethnic Uzbek from the southern Kyrgyz city of Osh, moved with his father to St Petersburg for work several years ago, according to neighbours in Osh.
In Russia, he worked with his father as a panel beater in a car repair shop, they said. An acquaintance from St Petersburg said Jalilov had worked for about a year in a chain of sushi restaurants. A second acquaintance said he was a fan of sambo, a form of martial arts popular in Russia.
Jalilov's page on VK has photographs showing him wearing stylish Western outfits in a restaurant with friends and smoking a hookah pipe.
He had an interest in religion. The page had links to a website in Russian called I Love Islam and another called IslamHouse.com, which said it aimed to help people get to know Islam.
Another VK page which belonged to Jalilov included links to a site featuring the sayings of Muhammad ibn Abd al-Wahhab, an 18th century preacher on whose teachings Wahhabism is based.
ISIS, with its grip on territory in Syria and Iraq weakening, has switched its focus to inspiring sympathisers elsewhere.
Avenging Russia for its role in the Syria conflict has been a prominent theme on the group's social media sites.
Shortly after Russia launched its military operation in support of Syrian President Bashar al-Assad in 2015, the group released a video where it threatened to attack Russia very soon, and said that "the blood will spill like an ocean".