A man holds a photo of a victim at the Technological Institute station in St. Petersburg, Russia, April 3, 2021. An explosion hit the St. Petersburg subway on April 3, 2017, killing 14 people and injuring over 50 others. (Photo by Irina Motina/Xinhua)

People lay flowers to commemorate victims at the Technological Institute station in St. Petersburg, Russia, April 3, 2021. An explosion hit the St. Petersburg subway on April 3, 2017, killing 14 people and injuring over 50 others. (Photo by Irina Motina/Xinhua)

People walk past flowers laid to commemorate victims at the Technological Institute station in St. Petersburg, Russia, April 3, 2021. An explosion hit the St. Petersburg subway on April 3, 2017, killing 14 people and injuring over 50 others. (Photo by Irina Motina/Xinhua)

People lay flowers to commemorate victims at the Technological Institute station in St. Petersburg, Russia, April 3, 2021. An explosion hit the St. Petersburg subway on April 3, 2017, killing 14 people and injuring over 50 others. (Photo by Irina Motina/Xinhua)

People walk past flowers laid to commemorate victims at the Technological Institute station in St. Petersburg, Russia, April 3, 2021. An explosion hit the St. Petersburg subway on April 3, 2017, killing 14 people and injuring over 50 others. (Photo by Irina Motina/Xinhua)