This is for the silence, not sure if it works on the root.
EDIT: It also does not grant kills, but I'm not sure if this is intentional.
Reproduction steps to do this are probably too complicated to carry out, but I suggest trying to do this with 2 friends in a custom. 2v1, get a friend on your team and the other, get the ally to damage the enemy to low health, place your E on them, allow ally to kill them. No assist should come of it.