BREAKING: Multiple casualties reported after attack on Russian concert hall

Witnesses say at least three men dressed in camouflage opened fire on people gathered for a show inside a Russian concert hall, killing several people inside. » Subscribe to MSNBC: Follow MSNBC Show Blogs MaddowBlog: ReidOut Blog: MSNBC delivers breaking news, in-depth analysis of politics headlines, as well as commentary and informed perspectives. Find video clips and segments from The Rachel Maddow Show, Morning Joe, The Beat with Ari Melber, Deadline: White House, The ReidOut, All In, Last Word, 11th Hour, and Alex Wagner who brings her breadth of reporting experience to MSNBC primetime. Watch “Alex Wagner Tonight” Tuesday through Friday at 9pm Eastern. Connect with MSNBC Online Visit : Subscribe to the MSNBC Daily Newsletter: Find MSNBC on Facebook: