LOL! Yeah, some Englishmen wanted to give the species a bum rap..lol. Actually, the following is the reason they are called a murder of crows:
One states that crows often will come together and "decide the capital fate of another crow." Another possible origin comes from people who view the "appearance of crows as an omen of death." Also, the phrase "murder of crows" comes from a time in history when groups of animals were described in different ways, according to the documentary's website.