Matthew Poole and continuators on Joshua 20:3

3 That the slayer that killeth any person unawares, and unwittingly , may flee thither: and they shall be your refuge from the avenger of blood .

Heb. Through Ignorance, or Error, or Mistake, and without Knowledg. The same thing twice repeated to cut off all the claims and expectations that Wilful Murderers might have of Protection here; and God having declared, That such should be taken even from his Altar, that they might be killed, Exod. 21. 14. and accordingly Ioab was by Solomons Order, killed even at the Altar, 1 King. 2. 28, 29, 30, 31, 34▪ it is the more strange and impudent, that any Christians should make their Sanctuaries give Protection to such persons whom God hath so expresly excepted from it, which the Papists do; and their Doctors are not ashamed to defend it upon frivolous reasons.

The Kins-man, who had right or power to demand, or take vengeance of the slaughter.