If Person A has known motive to kill Person B, in a "non-clean" hit Person A will immediately come under suspicion. If the hit is "clean", anything could have h

If Person A has known motive to kill Person B, in a "non-clean" hit Person A will immediately come under suspicion. If the hit is "clean", anything could have happened and it's a lot harder to establish it as a murder and therefore Person A has a much lower risk of being brought into the case.