Another reason was that russians wanted to show themselves as aliens to european world after being kicked out of G7 and closed investments made their economy slow down.
And one more reason was to make europeans concentrate on refugees problems and let Russia continue war in Ukraine without any problems from UNO.
And after every terrorist attack in Europe russian authorities are coming out and say "we want a profound dialogue about terrorism", though in many cases russian roots can be almost obvious especially from Chechnya, which leader is a dog to Putin.