Why is a group of crows called a murder?

This questions has been answered in great detail in this Quora post. Basically, the term has survived to modern English due to its inclusion in a Late Middle Age book called The Book of Saint Albans. There are several theories about its origin:

• For instance, there is a folktale that crows will gather and decide the capital fate of another crow.
• Many view the appearance of crows as an omen of death because ravens and crows are scavengers and are generally associated with dead bodies, battlefields, and cemeteries, and they’re thought to circle in large numbers above sites where animals or people are expected to soon die.
• But the term “murder of crows” mostly reflects a time when groupings of many animals had colorful and poetic names.