We know that a Goel haDam (blood avenger) has a special allowance to kill the rotzeach who accidentally killed his family member. The accidental rotzeach can avoid this fate by fleeing to an ir miklat, one of the designated cities of refuge.
But what if the Goel haDam is a shrewd/sneaky guy who is somehow able to gain access into this ir miklat and kills the rotzeach.
1) Do we say that he's a murderer, and thus subject to the death penalty, since the special allowance to kill expired once the rotzeach entered or is in the ir miklat?
2) Do we say the allowance to kill only expires when the Kohen Gadol dies and the ir miklat is more of a "home base" (like when playing tag) and it would be the ir miklat at fault for not preventing this/having better security?
Basically, I'd like to better understanding of the parameters for this unbelievable exception of allowance to kill that the Torah grants a person.