This Achievement can be obtained on the second level of the game "
Nakasendo Road".
The first of 3 accidents you can cause is in the center of the map there will be a guard standing next to an ox get close enough to use Hayato's stone on it this will cause the Ox to kick the guard killing him.
The second accident is to the left most part of the map there will be a loose rock sitting on an edge, you will need to climb up the vines near the center of the map and jump across the top of the wagons to reach it once the patroling gaurd is below it interact with the boulder and it will crush the guard.
The third and final accident is in the top most section of the map near the waters edge there will be a wagon with two blocks by the wheel get close enough to the wagon to interact with both blocks this will cause it to roll down hill killing the stationary officer and will cause the achievement to pop.