Because the witnesses had different viewpoints so they might have seen different things..
If for example the witness is somehow related to the victim, his/her point of view might have been compromised and couldn't be used
hope this helps
In logic, an entailment is the relationship between sentences whereby one sentence will be true if all the others are also true. Want a less-dry-sounding, real-life example? How about this: Being a good student, for instance, is an entailment of attending classes, learning the material, and keeping up with assignments. An old-fashioned definition of entailment is a set of limitations that restrict the ways property can be bequeathed to heirs.
Because of pollution and over hunting
Anthropologists are positioned uniquely positioned to study gender in any society because they focus on biological differences to see how the culture is constructed