Numbers 35:30-33

30Whoso killeth any personH5315, the murdererH7523 shall be slain at the mouthH6310 of witnessesH5707: but oneH259 witnessH5707 shall not testifyH6030 against any personH5315 that he dieH4191. 31Moreover ye shall takeH3947 no ransomH3724 for the lifeH5315 of a murdererH7523, that is guiltyH7563 of deathH4191; but he shall surely be putH4191 to deathH4191. 32And ye shall takeH3947 no ransomH3724 for him that is fledH5127 to his cityH5892 of refugeH4733, that he may come again to dwellH3427 in the landH776, until the deathH4194 of the priestH3548. 33So ye shall not polluteH2610 the landH776 wherein ye are: for bloodH1818, it polluteth the landH776; and no expiation can be made for the landH776 for the bloodH1818 that is shedH8210 therein, but by the bloodH1818 of him that shedH8210 it.