1,309. When a Kohein May Not Impurify Himself

202:12 If a kohein's relative separated himself from Judaism, the kohein does not render himself impure for him, nor does he do so for one who committed suicide. Anyone for whom one would not observe aveilus (mourning), a kohein likewise does not render himself impure. (This halacha does not take into account various mitigating circumstances. Consult your rabbi for cases of practical application.)

202:13 A kohein only renders himself impure for a relative whose body is whole, not when part is missing. Therefore, some authorities say that a kohein may not impurify himself for one who was killed, as this is considered to be missing a part. It is proper to act stringently in this matter.