The unlawful killing a believer is considered the same as killing all mankind 5:32
5:32 That was why We wrote for the Children of Israel that whoever killed a soul, except for a soul slain, or for sedition in the earth, it should be considered as though he had killed all mankind; and that whoever saved it should be regarded as though he had saved all mankind. Our Messengers brought them proofs; then many of them thereafter commit excesses in the earth.