The four men accused of carrying out the deadliest terror attack in Russia in nearly 20 years appeared in court on terrorism charges Sunday. More than 130 people were killed when the men allegedly opened fire at a concert hall near Moscow on Friday. An affiliate of the Islamic State group says it was behind the attack. CBS News national security contributor Sam Vinograd has more. CBS News Streaming Network is the premier 24/7 anchored streaming news service from CBS News and Stations, available free to everyone with access to the Internet. The CBS News Streaming Network is your destination for breaking news, live events and original reporting locally, nationally and around the globe. Launched in November 2014 as CBSN, the CBS News Streaming Network is available live in 91 countries and on 30 digital platforms and apps, as well as on CBSNews.com and Paramount+. Subscribe to the CBS News YouTube channel: https://youtube.com/cbsnews Watch CBS News: https://cbsnews.com/live/ Download the CBS News app: https://cbsnews.com/mobile/ Follow CBS News on Instagram: https://instagram.com/cbsnews/ Like CBS News on Facebook: https://facebook.com/cbsnews Follow CBS News on Twitter: https://twitter.com/cbsnews Subscribe to our newsletters: https://cbsnews.com/newsletters/ Try Paramount+ free: https://paramountplus.com/?ftag=PPM-05-10aeh8h For video licensing inquiries, contact: [email protected]