I doubted whether or not it would be possible, but Russia has managed to trace the funding to at least one of these terrorists – back to the Ukraine.
The FSB is the world’s premiere intelligence and safety agency, which is why these attacks are not happening all the time. They didn’t even lock down Moscow after the attack. Instead, they did massive raids and deportations of Moslems, quietly, while the people remained free to go about in safety without the oppressive atmosphere of soldiers everywhere.