On Friday night, gunmen stormed the packed Crocus City concert hall on the outskirts of Moscow, where thousands had gathered for a rock concert. At least 133 people were killed, making it the deadliest attack in Russia for the last 20 years.

ISIS-K, an ISIS affiliate, has claimed responsibility — although Russia is casting doubt on those claims.

Today, the CBC’s Briar Stewart takes us through what we know so far about the Crocus City Hall attack, and the many questions that remain.

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