People attend a religious service marking the 15th anniversary of the deadly school siege in the town of Beslan, Russia September 3, 2019. The inscription reads "We remember. 1-3.09.2004". REUTERS/Eduard Korniyenko 

A priest walks inside the building of a school, which was a place of the 2004 Beslan hostage crisis, on the days of the 15th anniversary of the siege, in the town of Beslan, Russia September 3, 2019. REUTERS/Eduard Korniyenko TPX IMAGES OF THE DAY 

A man mourns at the cemetery, where victims of the 2004 school siege are buried, on the days of the 15th anniversary of the siege, in the southern Russian town of Beslan, Russia, September 2, 2019. REUTERS/Eduard Korniyenko 

People visit the cemetery, where victims of the 2004 school siege are buried, on the days of the 15th anniversary of the siege, in the southern Russian town of Beslan, Russia, September 2, 2019. REUTERS/Eduard Korniyenko 

A view shows the Tree of Sorrow monument at the cemetery, where victims of the 2004 school siege are buried, on the days of the 15th anniversary of the siege, in the southern Russian town of Beslan, Russia, September 2, 2019. REUTERS/Eduard Korniyenko 

A woman mourns at the cemetery, where victims of the 2004 school siege are buried, on the days of the 15th anniversary of the siege, in the southern Russian town of Beslan, Russia, September 2, 2019. REUTERS/Eduard Korniyenko 

A man mourns at the cemetery, where victims of the 2004 school siege are buried, on the days of 15th anniversary of the siege, in the southern Russian town of Beslan, Russia, September 2, 2019. REUTERS/Eduard Korniyenko 

Women mourn at the cemetery, where victims of the 2004 school siege are buried, on the days of 15th anniversary of the siege, in the southern Russian town of Beslan, Russia, September 2, 2019. REUTERS/Eduard Korniyenko 

Children walk at the cemetery, where victims of the 2004 school siege are buried, on the days of the 15th anniversary of the siege, in the southern Russian town of Beslan, Russia, September 2, 2019. REUTERS/Eduard Korniyenko 

People attend a memorial event marking the 15th anniversary of the deadly school siege in the town of Beslan, Russia September 2, 2019. The inscription reads "We remember. 3.09.2004". REUTERS/Eduard Korniyenko 

Children attend a memorial event marking the 15th anniversary of the deadly school siege in the town of Beslan, Russia September 2, 2019. The inscription reads "We remember. 3.09.2004". REUTERS/Eduard Korniyenko 

A general view shows the cemetery, where victims of the 2004 school siege are buried in the southern Russian town of Beslan, Russia, April 13, 2017. REUTERS/Kazbek Basayev 

People attend a ceremony commemorating those who died during the 2004 Beslan hostage crisis at the southern Russian town's School Number One in Beslan, September 3, 2015. Moscow's campaign against Islamist insurgents reached a watershed in September 2004, when heavily armed Chechen gunmen seized a school in Beslan. When the siege ended three days later, 334 people - half of them children - were dead. REUTERS/Kazbek Basayev 

School children release balloons during a ceremony commemorating the victims of the 2004 Beslan hostage crisis in the southern Russian town of Beslan, September 3, 2015. Moscow's campaign against Islamist insurgents reached a watershed in September 2004, when heavily armed Chechen gunmen seized a school in Beslan. When the siege ended three days later, 334 people - half of them children - were dead. REUTERS/Kazbek Basayev 

People attend a religious service commemorating those who died during the 2004 Beslan hostage crisis at the southern Russian town's School Number One in Beslan, September 3, 2015. Moscow's campaign against Islamist insurgents reached a watershed in September 2004, when heavily armed Chechen gunmen seized a school in Beslan. When the siege ended three days later, 334 people - half of them children - were dead. REUTERS/Kazbek Basayev 

People mourn during a ceremony commemorating those who died during the 2004 Beslan hostage crisis at the southern Russian town's School Number One in Beslan, September 3, 2015. Moscow's campaign against Islamist insurgents reached a watershed in September 2004, when heavily armed Chechen gunmen seized a school in Beslan. When the siege ended three days later, 334 people - half of them children - were dead. REUTERS/Kazbek Basayev 

People attend a religious service commemorating those who died during the 2004 Beslan hostage crisis at the southern Russian town's School Number One in Beslan, September 3, 2015. Moscow's campaign against Islamist insurgents reached a watershed in September 2004, when heavily armed Chechen gunmen seized a school in Beslan. When the siege ended three days later, 334 people - half of them children - were dead. REUTERS/Kazbek Basayev 

A woman mourns during a ceremony commemorating the people who died during the 2004 Beslan hostage crisis at the southern Russian town's School Number One in Beslan, September 3, 2008. Moscow's campaign against Islamist insurgents reached a watershed in September 2004, when heavily armed Chechen gunmen seized a school in Beslan. When the siege ended three days later, 334 people - half of them children - were dead. REUTERS/Kazbek Basayev 

A woman mourns during a ceremony commemorating the people who died during the 2004 Beslan hostage crisis at the southern Russian town's School Number One in Beslan, September 3, 2015. Moscow's campaign against Islamist insurgents reached a watershed in September 2004, when heavily armed Chechen gunmen seized a school in Beslan. When the siege ended three days later, 334 people - half of them children - were dead. REUTERS/Kazbek Basayev 

People hold a banner with photographs of the victims of the Beslan school in front of 334 candles arranged to spell "Beslan", during a remembrance event in St.Petersburg September 3, 2014. People gathered on Wednesday to mark the anniversary of the 2004 Beslan school siege by Islamic militants in North Ossetia that resulted in 334 civilian deaths, including 186 children. REUTERS/Alexander Demianchuk (RUSSIA - Tags: CRIME LAW ANNIVERSARY) 

Activists light some of the 334 candles arranged to spell "Beslan", during an event in St.Petersburg, commemorating the victims of the 2004 hostage crisis in the southern Russian town of Beslan, September 3, 2014. People gathered on Wednesday to mark the anniversary of the 2004 Beslan school siege by Islamic militants in North Ossetia that resulted in 334 civilian deaths, including 186 children. REUTERS/Alexander Demianchuk (RUSSIA - Tags: CRIME LAW ANNIVERSARY TPX IMAGES OF THE DAY) 

People mourn inside School Number One during a ceremony commemorating the victims of the 2004 hostage crisis in the southern Russian town of Beslan, September 3, 2014. People marked the anniversary of the siege at a local school in 2004 that resulted in 334 civilian deaths, including 186 children. REUTERS/Kazbek Basayev (RUSSIA - Tags: CRIME LAW ANNIVERSARY) 

People grieve at the cemetery in the southern Russian town of Beslan, September 3, 2014. People marked the anniversary of the siege at a local school in 2004 that resulted in 334 civilian deaths, including 186 children. REUTERS/Kazbek Basayev (RUSSIA - Tags: CRIME LAW ANNIVERSARY) 

School children release balloons during a ceremony commemorating the victims of the 2004 hostage crisis in the southern Russian town of Beslan, September 3, 2014. The people of Beslan in southern Russia marked the anniversary of the siege at a local school in 2004 that resulted in 334 civilian deaths, including 186 children. REUTERS/Kazbek Basayev (RUSSIA - Tags: CRIME LAW ANNIVERSARY) 

Women grieve at the cemetery in the southern Russian town of Beslan, September 1, 2014. The people of Beslan in southern Russia marked the anniversary of the siege at a local school in 2004 that resulted in 334 civilian deaths, including 186 children. REUTERS/Kazbek Basayev (RUSSIA - Tags: CRIME LAW ANNIVERSARY CIVIL UNREST) 

People mourn inside School Number One during a ceremony commemorating the victims of the 2004 hostage crisis in the southern Russian town of Beslan, September 1, 2014. REUTERS/Kazbek Basayev (RUSSIA - Tags: CRIME LAW ANNIVERSARY CIVIL UNREST TPX IMAGES OF THE DAY) 

Candles and flowers are placed in front of a banner with photographs of victims of the Beslan school siege during a rememberence event held by the youth movement of the Yabloko political party in St.Petersburg September 3, 2012. Russians on Monday marked the anniversary of the 2004 Beslan school siege by Islamic militants in North Ossetia, in which over 330 people died, more than half of them children. REUTERS/Alexander Demianchuk (RUSSIA - Tags: ANNIVERSARY CIVIL UNREST POLITICS) 

An activist from the youth movement of the Yabloko political party lights some of the 334 candles arranged to spell "Beslan" during a rememberence event in St.Petersburg September 3, 2012. Russians on Monday marked the anniversary of the 2004 Beslan school siege by Islamic militants in North Ossetia, in which over 330 people died, more than half of them children. REUTERS/Alexander Demianchuk (RUSSIA - Tags: ANNIVERSARY POLITICS CIVIL UNREST) 

Workers build a monument around a building at School Number 1 in the North Ossetian town of Beslan August 18, 2011. Russia will mark the anniversary of the 2004 Beslan school siege by Islamic militants in North Ossetia, in which over 330 people died, more than half of them children, on September 1. REUTERS/Kazbek Basayev (RUSSIA - Tags: CRIME LAW CIVIL UNREST ANNIVERSARY EDUCATION) 

Workers build a monument around a building at School Number 1 in the North Ossetian town of Beslan August 18, 2011. Russia will mark the anniversary of the 2004 Beslan school siege by Islamic militants in North Ossetia, in which over 330 people died, more than half of them children, on September 1. REUTERS/Kazbek Basayev (RUSSIA - Tags: CRIME LAW CIVIL UNREST ANNIVERSARY EDUCATION) 

Workers build a monument around a building at School Number 1 in the North Ossetian town of Beslan August 18, 2011. Russia will mark the anniversary of the 2004 Beslan school siege by Islamic militants in North Ossetia, in which over 330 people died, more than half of them children, on September 1. REUTERS/Kazbek Basayev (RUSSIA - Tags: CRIME LAW CIVIL UNREST ANNIVERSARY EDUCATION) 

Workers build a monument around at building at School Number 1 in the North Ossetian town of Beslan August 18, 2011. Russia will mark the anniversary of the 2004 Beslan school siege by Islamic militants in North Ossetia, in which over 330 people died, more than half of them children, on September 1. REUTERS/Kazbek Basayev (RUSSIA - Tags: CRIME LAW CIVIL UNREST ANNIVERSARY EDUCATION) 

People mourn inside School Number One during a ceremony commemorating the people who died in the 2004 hostage crisis in the southern Russian town of Beslan, September 3, 2010. The people of Beslan in southern Russia marked the anniversary of the siege at a local school in 2004 that resulted in 334 civilian deaths, including 186 children. REUTERS/Kazbek Basayev (RUSSIA - Tags: CRIME LAW ANNIVERSARY) 

Women grieve at the cemetery in the southern Russian town of Beslan, September 3, 2010. The people of Beslan in southern Russia marked the anniversary of the siege at a local school in 2004 that resulted in 334 civilian deaths, including 186 children. REUTERS/Kazbek Basayev (RUSSIA - Tags: CRIME LAW ANNIVERSARY) 

A woman grieves at the cemetery in the southern Russian town of Beslan, September 3, 2010. The people of Beslan in southern Russia marked the anniversary of the siege at a local school in 2004 that resulted in 334 civilian deaths, including 186 children. REUTERS/Kazbek Basayev (RUSSIA - Tags: CRIME LAW ANNIVERSARY IMAGES OF THE DAY) 

People grieve at the cemetery in the southern Russian town of Beslan, September 3, 2010. The people of Beslan in southern Russia marked the anniversary of the siege at a local school in 2004 that resulted in 334 civilian deaths, including 186 children. REUTERS/Kazbek Basayev (RUSSIA - Tags: CRIME LAW ANNIVERSARY) 

People mourn during a ceremony commemorating those who died in the 2004 hostage crisis at school number one in the southern Russian town of Beslan September 1, 2010. One thousand children and parents were taken hostage by Chechen separatists on the first day of the new school year on September 1, 2004. After three days of siege, Russian forces stormed the school and some of the rebels blew themselves up. A total of 333 hostages -- more than half of them children -- were killed in the chaos and hundreds were wounded. Picture taken September 1, 2010. REUTERS/Kazbek Basayev (RUSSIA - Tags: CRIME LAW ANNIVERSARY) 

A woman looks at pictures of people who died in a 2004 hostage crisis inside school number one in the southern Russian town of Beslan September 1, 2010. One thousand children and parents were taken hostage by Chechen separatists on the first day of the new school year on September 1, 2004. After three days of siege, Russian forces stormed the school and some of the rebels blew themselves up. A total of 333 hostages -- more than half of them children -- were killed in the chaos and hundreds were wounded. Picture taken September 1, 2010. REUTERS/Kazbek Basayev (RUSSIA - Tags: CRIME LAW ANNIVERSARY IMAGES OF THE DAY) 

People mourn inside School Number One during a ceremony commemorating the victims of the 2004 hostage crisis in the southern Russian town of Beslan, September 1, 2010. One thousand children and parents were taken hostage by Chechen separatists on the first day of the new school year on September 1, 2004. After three days of siege, Russian forces stormed the school and some of the rebels blew themselves up. A total of 333 hostages -- more than half of them children -- were killed in the chaos and hundreds were wounded. REUTERS/Kazbek Basayev (RUSSIA - Tags: CRIME LAW ANNIVERSARY) 

People mourn inside School Number One during a ceremony commemorating the victims of the 2004 hostage crisis in the southern Russian town of Beslan, September 1, 2010. One thousand children and parents were taken hostage by Chechen separatists on the first day of the new school year on September 1, 2004. After three days of siege, Russian forces stormed the school and some of the rebels blew themselves up. A total of 333 hostages -- more than half of them children -- were killed in the chaos and hundreds were wounded. REUTERS/Kazbek Basayev (RUSSIA - Tags: CRIME LAW ANNIVERSARY) 

People mourn inside School Number One during a ceremony commemorating the victims of the 2004 hostage crisis in the southern Russian town of Beslan, September 1, 2010. One thousand children and parents were taken hostage by Chechen separatists on the first day of the new school year on September 1, 2004. After three days of siege, Russian forces stormed the school and some of the rebels blew themselves up. A total of 333 hostages -- more than half of them children -- were killed in the chaos and hundreds were wounded. REUTERS/Kazbek Basayev (RUSSIA - Tags: CRIME LAW ANNIVERSARY EDUCATION) 

People mourn inside School Number One during a ceremony commemorating the victims of the 2004 hostage crisis in the southern Russian town of Beslan, September 1, 2010. One thousand children and parents were taken hostage by Chechen separatists on the first day of the new school year on September 1, 2004. After three days of siege, Russian forces stormed the school and some of the rebels blew themselves up. A total of 333 hostages -- more than half of them children -- were killed in the chaos and hundreds were wounded. REUTERS/Kazbek Basayev (RUSSIA - Tags: CRIME LAW ANNIVERSARY) 

The Head of the new North Caucasus Federal District Alexander Khloponin holds flowers as he visits a cemetery in Beslan, February 23, 2010. Around 1000 children and parents were taken hostage by Chechen separatists on the first day of the new school year on September 1, 2004. After three days of siege, Russian forces stormed the school and some of the rebels blew themselves up. A total of 333 hostages -- more than half of them children -- were killed in the chaos and hundreds were wounded. REUTERS/Kazbek Basayev (RUSSIA - Tags: MILITARY POLITICS CRIME LAW) 

Children release 334 balloons into the air, symbolising the people who died in the 2004 hostage crisis in Beslan September 3, 2008. Moscow's campaign against Islamist insurgents reached a watershed in September 2004, when heavily armed Chechen gunmen seized a school in Beslan. When the siege ended three days later, 334 people - half of them children - were dead. REUTERS/Sergei Karpukhin (RUSSIA) 

A man in uniform attends a ceremony to commemorate the people who died during the 2004 Beslan hostage crisis in the southern Russian town's school number 1 on September 3, 2008. Moscow's campaign against Islamist insurgents reached a watershed in September 2004, when heavily armed Chechen gunmen seized a school in Beslan. When the siege ended three days later, 334 people - half of them children - were dead. REUTERS/Sergei Karpukhin (RUSSIA) 

Carnations cover the floor of school number one during a ceremony commemorating the people who died during the 2004 hostage crisis in the southern Russian town of Beslan September 3, 2008. Moscow's campaign against Islamist insurgents reached a watershed in September 2004, when heavily armed Chechen gunmen seized a school in Beslan. When the siege ended three days later, 334 people - half of them children - were dead. REUTERS/Sergei Karpukhin (RUSSIA) 

Women mourn during a ceremony commemorating the people who died during the 2004 Beslan hostage crisis in the southern Russian town's school number 1, September 3, 2008. Moscow's campaign against Islamist insurgents reached a watershed in September 2004, when heavily armed Chechen gunmen seized a school in Beslan. When the siege ended three days later, 334 people - half of them children - were dead. REUTERS/Sergei Karpukhin (RUSSIA) 

People react during a ceremony commemorating the people who died during the 2004 Beslan hostage crisis in the southern Russian town's school number 1, September 3, 2008. Moscow's campaign against Islamist insurgents reached a watershed in September 2004, when heavily armed Chechen gunmen seized a school in Beslan. When the siege ended three days later, 334 people - half of them children - were dead. REUTERS/Sergei Karpukhin (RUSSIA) 

A woman reacts during a ceremony commemorating the people who died during the 2004 Beslan hostage crisis in the southern Russian town's school number 1, September 3, 2008. Moscow's campaign against Islamist insurgents reached a watershed in September 2004, when heavily armed Chechen gunmen seized a school in Beslan. When the siege ended three days later, 334 people - half of them children - were dead. REUTERS/Sergei Karpukhin (RUSSIA) 

Relatives grieve at the cemetery in Russia's town of Beslan September 1, 2008. The people of Beslan in southern Russia marked the anniversary of the siege at a local school in 2004 that resulted in 334 civilian deaths, including 186 children. REUTERS/Sergei Karpukhin (RUSSIA) 

Relatives grieve at the cemetery in Russia's town of Beslan September 1, 2008. The people of Beslan in southern Russia marked the anniversary of the siege at a local school in 2004 that resulted in 334 civilian deaths, including 186 children. REUTERS/Sergei Karpukhin (RUSSIA) 

A woman grieves at the cemetery in Russia's town of Beslan September 1, 2008. The people of Beslan in southern Russia marked the anniversary of the siege at a local school in 2004 that resulted in 334 civilian deaths, including 186 children. REUTERS/Sergei Karpukhin (RUSSIA) 

Relatives grieve at the cemetery in Russia's town of Beslan September 1, 2008. The people of Beslan in southern Russia marked the anniversary of the siege at a local school in 2004 that resulted in 334 civilian deaths, including 186 children. REUTERS/Sergei Karpukhin (RUSSIA) 

RNPS IMAGES OF THE YEAR 2007 - A soft toy lies amid flowers in the burned-out gymnasium of Beslan's School No. 1, the scene of a 2004 hostage crisis, on the anniversary of the siege late September 1, 2007. President Vladimir Putin said Russia could not forget the Beslan tragedy but his words fell on deaf ears as the mothers of the dead children accused the government of being complicit in the deaths. REUTERS/Eduard Korniyenko (RUSSIA) 

Vitaly Kaloyev (L), who was convicted of killing an air traffic controller linked to a 2002 mid-air collision, comforts a woman who lost a relative in the 2004 Beslan school siege at the cemetery in Beslan in southern Russia November 14, 2007. Kaloyev was released from jail and flew back to Russia on Monday. Kaloyev, who lost his wife and children in the crash, had expected to be set free after a Swiss court last week upheld a ruling to cut his sentence to five years and three months, of which he had already served two-thirds. REUTERS/Eduard Korniyenko (RUSSIA) 

Vitaly Kaloyev (L), who was convicted of killing an air traffic controller linked to a 2002 mid-air collision, comforts a woman who lost a relative in the 2004 Beslan school siege at a cemetery in Beslan in southern Russia November 14, 2007. Kaloyev was released from jail and flew back to Russia on Monday. Kaloyev, who lost his wife and children in the crash, had expected to be set free after a Swiss court last week upheld a ruling to cut his sentence to five years and three months, of which he had already served two-thirds. REUTERS/Eduard Korniyenko (RUSSIA) 

A woman grieves beside the grave of a victim of the 2004 Beslan school siege in a cemetery in Beslan late September 1, 2007. President Vladimir Putin said on Saturday Russia could not forget the Beslan tragedy but his words fell on deaf ears as the mothers of the dead children accused the government of being complicit in the deaths. Picture taken September 1, 2007. REUTERS/Eduard Korniyenko (RUSSIA) 

A woman lights candles in front of victims' portraits in the burned-out gymnasium of Beslan's School No. 1, the scene of a 2004 hostage crisis, on the anniversary of the siege late September 1, 2007. President Vladimir Putin said on Saturday Russia could not forget the Beslan tragedy but his words fell on deaf ears as the mothers of the dead children accused the government of being complicit in the deaths. Picture taken September 1, 2007. REUTERS/Eduard Korniyenko (RUSSIA)