Ok, so Alexander II was killed by the actions of Gribovitsky and Rysakov, who indeed tried to throw a bomb and failed. Bomb supposed to fell under carriage and, frankly I don't remember how things go awry, but bomb exploded behind the carriage, tsar was a-ok. Yet, probably in hubris, despite the advise of his bodyguards, he gets out of carriage, go ask Rysakov something, and it gives the second terrorist Gribovitskiy chance to throw another, smaller bomb. It lands by the Emperors legs. Explosion that follows gravely injures the monarch (his legs are shattered) and Gribovitsky himself. Bodyguards then carry the Emperor to the sled, to bring him to the Winter Palace to die, as he asked them.
If my memory does not deceive me, 11 people were injured. One of the bodyguards killed, along with 14 yo boy from the street, from the first explosion. Second explosion killed the Emperor and his killer.
Later captured Rysakov gives away all the members of "Narodnaya Volya", and in following months organisation ceased to exist completely. There were no wanted posters for someone who killed the Tsar.