Ongoing discussion of a guilty party intermingled with innocent people (for example). Beginning with a case of two people standing together - and an arrow being shot from there those two people are, which kills someone. But since there's no way to identify which of those two shot the arrow, both are off the hook. Even if one of them is so righteous (like Abba Halafta) that the perpetrator seems obvious. Also, a group of those who all are waiting for their respective death sentences, but the executions are different, so how do you establish which should be put to death how? Look to the majority of the death sentences for the group and also the ranking of the severity of the different executions, to determine which should be applied to all.