There is a related word, scapegoat, which means:
scapegoat (noun) A person who is blamed for the wrongdoings, mistakes, or faults of others, especially for reasons of expediency.
From this word, we have the word scapegoater, which means:
scapegoater one that makes a scapegoat of something or somebody
While scapegoat is fairly common in the vernacular, I think scapegoater is a less common word. However, it fits what you are looking for.
Here's a usage of it in print:
Tolerance and independent thinking are essential to a democratic form of government, but the scapegoater cannot think straight.
(Charles Henry Scherf, Do You Own Thinking, 1946)
Another book about hostilities in the workplace says:
A scapegoater is one who transfers blame to persons or groups, who are not necessarily guilty, in order to focus attention away from those who are actually responsible — sometimes from themselves.
(J.A. Wambach & R.W. Fuller, Battles between somebodies and nobodies: stop abuse of rank at work and at home, 2008)