Here "blood" represents a person's death. The phrase "on him" is an idiom that means that person is considered responsible. AT: "it will be his own fault that he dies"
Here "blood" represents a person's death. The phrase "I will require his blood from" is an idiom that means to consider someone responsible. AT: "I will consider that person's death to be the fault of the watchman" (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-idiom]])