The only "successful" resistance to state murders that I'm aware of (and resistance here is considered mutually exclusive of the solution that would be the destruction of the state) besides working through the system is a diversity of action that exacts a real cost in response to or anticipation of a murder.
A heavy enough backlash can act as a future deterrent. Of course, these actions are usually not taken in order to be a deterrent, but are a natural outpouring of vengeful rage.
For more on this, I'd suggest texts on the subject of revolutionary solidarity, but also the words and actions of anarchists in Chile, because many comrades there have been murdered by the democratic state in recent memory, not to mention under the former dictatorship.
P.S. The idea of "success" here deserves to be questioned, since nothing yet has returned the life destroyed by the State.
