Is this synagogue's guard unarmed? Seems to me the guard should be prepared for this sort of thing, especially given that Moscow is not exactly a low-crime area, even apart from anti-Semitic and Chechnyan terrorist types. Anyone approaching an orthodox synagogue with a shaved head and wearing a leather jacket ought to be looking down the barrel of a gun before he's anywhere near close enough to stab anybody -- seems like it would be pretty obvious from at least 20 yards away that he had no legitimate business there.
Sadly looking down the barrel of a gun isn't very likely unless they bribe a cop to hang around.