A possible correction to Woundweavr's writeup. Everything he said is true with the possible exception of, "The tsar Nicholas II ordered his troops to open fire." Nicholas II was not in St. Petersburg at the time of the demonstration. Short of any standing orders given to the palace guard (which haven't been found if they were documented), he couldn't have given an order to fire.

This is how the event has been described in the books I have read. As always, history is murky territory, so I may be wrong.