Russia was observing a national day of mourning on Sunday for victims of a fiery terrorist attack on a suburban Moscow concert venue, as the death toll climbed to 137 and questions lingered about the identities and motives of the perpetrators. Here’s what to know about the attack and its aftermath. https://nyti.ms/4a456Dh

Moscow Concert Hall Shooting Updates: Russia Observes Day of Mourning for Victims - The New York Times

Moscow Concert Hall Shooting Updates: Russia Observes Day of Mourning for Victims - The New York Times

American officials attribute Friday’s attack in a Moscow suburb, which killed at least 137 people, to a branch of the Islamic State active in Iran and Afghanistan.