On a Friday night in a northwestern suburb of Moscow, hundreds of music lovers were waiting in anticipation for a performance from progressive rock band Picnic.As the clamour and noise grew louder for the artists to take to the stage at Crocus City Hall, a sprawling shopping mall and music venue, a devastating act of violence was carried out that left more than 130 people dead and dozens more injured. It is the deadliest attack in Russia since the 2004 Beslan school siege, when terrorists killed 334 people.