I have another question for you. Is that reward limited to only witches and wizards? Could a vampire or werewolf or even a goblin try for it? Cause I think one of them will have a better chance at succeeding in killing Bella than anyone else. I also do wonder if Bella just goes into the wrong muggle house and tries to kill a old retired paranoid muggle who always carries a gun and get shot right between the eyes does he get the money? In pounds of course.
Anyone could claim it, but how would a Muggle know about the reward in the first place? Remember, the body has to be turned over to a Gringotts branch.
For those interested in the practice, read up on the Dictator Sulla and the idea of proscription