One of the men blamed by authorities in Kazakhstan for an armed raid on a national guard base, the deadliest attack in the country's history, had posted a video online that was sympathetic to Islamic State.
The video, posted on the social media page of Rustem Omarov, represents the first time Islamic State ideology has been linked to an act of militant violence in Kazakhstan, central Asia's wealthiest country and a major oil producer.
People from Kazakhstan and other central Asian states are fighting for Islamic State in Syria. There was no evidence the attack was ordered by the group, but its methods and ideology could threaten the already volatile region, which is mainly Muslim, has repressive governments and millions of people living in poverty.
Kazakhstan's president, Nursultan Nazarbayev, said on Wednesday the attackers had received instructions from abroad and were adherents of a pseudo-religious movement, though he did not identify it.
Omarov was one of more than 20 men who, according to the Kazakh authorities, were behind a "terrorist attack" in the north-western city of Aktobe. Nineteen people were killed in the attack on two gun shops and a national guard base on Sunday and its aftermath on Monday, including many of the attackers.
A person with the same name has an account on VKontakte, a social media network similar to Facebook that is popular in Russian-speaking countries.
That account posted a video which featured the Islamic State flag, an Arabic inscription on a black background.
In the video, a Russian-speaking narrator described how sometimes true believers in Islam have to follow their faith even if it means being cast out by their family as extremists.
The video, posted some time between April 8 and June 5, when Omarov last logged on, was uploaded from the account of a group called Paradise under the Shade of Sabres, which routinely promotes Islamic State online.
Kazakhstan is the biggest ex-Soviet oil producer after Russia. Foreign energy majors including ENI, Chevron and BG Group have production-sharing deals for Kazakh oil and gas fields.
There are oil fields in Aktobe region, some of which are being developed by Chinese and Korean oil firms, but none were affected by the attacks.
The Kazakh authorities have not officially named Omarov as one of the attackers in Aktobe. But his was one of the names on a list of suspects drawn up by the police and leaked to Kazakh media.
Reuters confirmed the authenticity of the list by visiting the addresses given for several other people on the list and talking to relatives or neighbours.
It was not possible to visit the address given for Omarov, because it was in a remote village, called Terensay. A local official in the village, contacted by phone, confirmed Omarov was registered there and had been sought by police over the attack.
It was not clear if Kazakh police had captured or killed Omarov. He was not among the suspected attackers who the police said were still at large.
The account on VKontakte for Rustem Omarov listed his location as Aktobe, and another person on the leaked police list of suspected attackers, Arsen Tanatarov, was a subscriber to Omarov's page.
The date of birth given for Omarov on the leaked police list was Dec. 1, 1990, while the date of birth on Omarov's VKontakte account was Dec. 5, 1990. It was not clear why there was a discrepancy.
Nazarbayev, the Kazakh president, designated Thursday as a day of mourning for the victims of the Aktobe attacks.
He ordered security forces to detain those attackers still on the run, and to "destroy" them if they put up any resistance, according to the presidential web site.
In the aftermath of the shooting in Aktobe, which is about 100 km (60 miles) from the Russian border, Kazakh officials described a coordinated series of attacks on the two commercial gun shops and then on the national guard base.
Andrei Grozin, a senior research fellow at Moscow's Institute of Oriental Studies, said it was possible the Aktobe attackers were an Islamic State sleeper cell, or simply people who associated themselves with the group.
"These are people who may not be connected in a 'superior-subordinate' relationship with the so-called Caliphate, but people who are mentally linked, who share their point of view and take up arms," said Grozin.
(Additional reporting by Maria Tsvetkova in MOSCOW and Raushan Nurshayaeva in ASTANA; Writing by Christian Lowe; Editing by Philippa Fletcher)