Director of FederalSecurity Bureau (FSB) said on 17^th that bomb attack was the truereason of plane crash in Sinai Pen. President of Russia, Putin expressedthe determination to trace and arrest the murderer on the same day, and saidthat Russia would step up its crackdown against ISIS in Syria and its terroristorganizations. Russian Airbus A321 was attacked by bomb after taking off, thenbroke up in the air. That was a homemade bomb, contained explosive from foreign country, explosiveequivalent 1kg TNT.