RebE > Why isn’t the first pair afraid that a second pair will come
First pair decided to go to court and accuse someone. They have time to case a victim and find an appropriate time where they are not likely to be seen by others. It is like pickpocket, or Putin on the border with Ukraine – they choose where and when. So, having a second pair is not very likely.
Second pair are people who happen to see a specific two people (first pair) at the specific time (of the crime). They were not able to choose a moment and location that will ensure their alibi. All following pairs are the same.